EMBRYOPSIDA Pirani & Prado
Gametophyte dominant, independent, multicellular, thalloid, with single-celled apical meristem, showing gravitropism; rhizoids +, unicellular; flavonoids + [absorbtion of UV radiation]; protoplasm dessication tolerant [plant poikilohydric]; cuticle +; cell walls with (1->4)-ß-D-glucans [xyloglucans], lignin +; several chloroplasts per cell; glycolate metabolism in leaf peroxisomes [glyoxysomes]; centrioles in vegetative cells 0, metaphase spindle anastral, predictive preprophase band of microtubules, phragmoplast + [cell wall deposition spreading from around the spindle fibres], plasmodesmata +; antheridia and archegonia jacketed, stalked; spermatogenous cells monoplastidic, centrioles develop de novo, associated with basal bodies of flagellae, multilayered structure +, proximal end of basal bodies lacking symmetry, stellate pattern associated with doublet tubules of transition zone; spermatozoids with a left-handed coil; male gametes with 2 lateral flagellae; oogamy; diploid embryo initially surrounded by haploid gametophytic tissue, plane of first division horizontal [with respect to long axis of archegonium/embryo sac], suspensor/foot +, cell walls with nacreous thickenings; sporophyte multicellular, sporangium +, single, with polar transport of auxin, dehiscence longitudinal; meiosis sporic, monoplastidic, microtubule organizing centre associated with plastid, cytokinesis simultaneous, preceding nuclear division, sporocytes 4-lobed, with a quadripolar microtubule system; spores in tetrads, sporopollenin in the spore wall, wall with several trilamellar layers [white-line centred layers, i.e. walls multilamellate]; close association between the trnLUAA and trnFGAA genes on the chloroplast genome.
Many of the bolded characters in the characterization above are apomorphies of subsets of streptophytes along the lineage leading to the embryophytes, not apomorphies of crown-group embryophytes per se.
All groups below are crown groups, nearly all are extant; characters mentioned are those of the common ancestor of the group.
Abscisic acid, ?D-methionine +; sporangium with seta, seta developing from basal meristem [between epibasal and hypobasal cells], sporangial columella + [developing from endothecial cells]; stomata +, anomocytic, cell lineage that produces them with symmetric divisions [perigenous]; underlying similarities in the development of conducting tissue and in rhizoids/root hairs; spores trilete; polar transport of auxins and class 1 KNOX genes expressed in the sporangium alone; MIKC, MI*K*C* and class 1 and 2 KNOX genes, post-transcriptional editing of chloroplast genes; gain of three group II mitochondrial introns.
[Anthocerophyta + Polysporangiophyta]: archegonia embedded/sunken in the gametophyte; sporophyte long-lived, chlorophyllous, nutritionally largely independent of the gametophyte; sporophyte-gametophyte junction interdigitate, sporophyte cells showing rhizoid-like behaviour.
Sporophyte well developed, branched, free living, sporangia several; spore walls not multilamellate [?here]; apical meristem +.
EXTANT TRACHEOPHYTA / VASCULAR PLANTS
Photosynthetic red light response; water content of protoplasm relatively stable [plant homoiohydric]; control of leaf hydration passive; (condensed or nonhydrolyzable tannins/proanthocyanidins +); vascular tissue +, sieve cells + [nucleus degenerating], tracheids +, in both protoxylem and metaxylem; endodermis +; root xylem exarch [development centripetal]; stem with an apical cell; branching dichotomous; leaves spirally arranged, blades with mean venation density 1.8 mm/mm2 [to 5 mm/mm2]; sporangia adaxial on the sporophyll, derived from periclinal divisions of several epidermal cells, wall multilayered [eusporangium]; columella 0; tapetum glandular; gametophytes exosporic, green, photosynthetic; stellate pattern split between doublet and triplet regions of transition zone; placenta with single layer of transfer cells in both sporophytic and gametophytic generations, embryonic axis not straight [root lateral with respect to the longitudinal axis; plant homorhizic].[MONILOPHYTA + LIGNOPHYTA]
Branching ± monopodial; lateral roots +, endogenous, root apex multicellular, root cap +; tracheids with scalariform-bordered pits; leaves with apical/marginal growth, venation development basipetal, growth determinate; sporangia borne in pairs and grouped in terminal trusses, dehiscence longitudinal, a single slit; cells polyplastidic, microtubule organizing centres not associated with plastids, diffuse, perinuclear; male gametes multiflagellate, basal bodies staggered, blepharoplasts paired; chloroplast long single copy ca 30kb inversion [from psbM to ycf2].
Plant woody; lateral root origin from the pericycle; branching lateral, meristems axillary; cork cambium + [producing cork abaxially], vascular cambium bifacial [producing phloem abaxially and xylem adaxially].
EXTANT SEED PLANTS / SPERMATOPHYTA
Plant evergreen; nicotinic acid metabolised to trigonelline, (cyanogenesis via tyrosine pathway); primary cell walls rich in xyloglucans and/or glucomannans, 25-30% pectin [Type I walls]; lignins derived from (some) sinapyl and particularly coniferyl alcohols [hence with p-hydroxyphenyl and guaiacyl lignin units, so no Maüle reaction]; root with xylem and phloem originating on alternate radii, vascular tissue not medullated, cork cambium deep seated; arbuscular mycorrhizae +; shoot apical meristem interface specific plasmodesmatal network; stem with vascular cylinder around central pith [eustele], phloem abaxial [ectophloic], endodermis 0, xylem endarch [development centrifugal]; wood homoxylous, tracheids and rays alone, tracheid/tracheid pits circular, bordered; mature sieve tube/cell lacking functioning nucleus, sieve tube plastids with starch grains; phloem fibres +; stem cork cambium superficial; branches exogenous; leaves with single trace from vascular sympodium [nodes 1:1]; stomatal pore with active opening in response to leaf hydration, control by abscisic acid, metabolic regulation of water use efficiency, etc.; leaves with petiole and lamina, development basipetal, blade simple; axillary buds +, (not associated with all leaves); prophylls two, lateral; plant heterosporous, sporangia borne on sporophylls; microsporophylls aggregated in indeterminate cones/strobili; true pollen +, grains mono[ana]sulcate, exine and intine homogeneous; ovules unitegmic, parietal tissue 2+ cells across, megaspore tetrad linear, functional megaspore single, chalazal, lacking sporopollenin, megasporangium indehiscent; pollen grains landing on ovule; male gametophyte development initially endosporic, lacking chlorophyll, tube developing from distal end of grain, gametes two, developing after pollination, with cell walls; female gametophyte endosporic, initially syncytial, walls then surrounding individual nuclei; seeds "large" [ca 8 mm3], but not much bigger than ovule, with morphological dormancy; embryo cellular ab initio, endoscopic, plane of first cleavage of zygote transverse, suspensor +, short-minute, embryonic axis straight [shoot and root at opposite ends; plant allorhizic], white, cotyledons 2; plastid transmission maternal; ycf2 gene in inverted repeat, whole nuclear genome duplication [zeta duplication], two copies of LEAFY gene, PHY gene duplications [three - [BP [A/N + C/O]] - copies], nrDNA with 5.8S and 5S rDNA in separate clusters; mitochondrial nad1 intron 2 and coxIIi3 intron and trans-spliced introns present.
ANGIOSPERMAE / MAGNOLIOPHYTA
Lignans, O-methyl flavonols, dihydroflavonols, triterpenoid oleanane, apigenin and/or luteolin scattered, [cyanogenesis in ANITA grade?], S [syringyl] lignin units common [positive Maüle reaction - syringyl:guaiacyl ratio more than 2-2.5:1], and hemicelluloses as xyloglucans; root apical meristem intermediate-open; root vascular tissue oligarch [di- to pentarch], lateral roots arise opposite or immediately to the side of [when diarch] xylem poles; origin of epidermis with no clear pattern [probably from inner layer of root cap], trichoblasts [differentiated root hair-forming cells] 0, exodermis +; shoot apex with tunica-corpus construction, tunica 2-layered; reaction wood ?, associated gelatinous fibres [g-fibres] with innermost layer of secondary cell wall rich in cellulose and poor in lignin; starch grains simple; primary cell wall mostly with pectic polysaccharides, poor in mannans; tracheid:tracheid [end wall] plates with scalariform pitting, wood parenchyma +; sieve tubes enucleate, sieve plate with pores (0.1-)0.5-10< µm across, cytoplasm with P-proteins, cytoplasm not occluding pores of sieve plate, companion cell and sieve tube from same mother cell; sugar transport in phloem passive; nodes 1:?; stomata brachyparacytic [ends of subsidiary cells level with ends of pore], outer stomatal ledges producing vestibule, reduction in stomatal conductance to increasing CO2 concentration; lamina formed from the primordial leaf apex, margins toothed, development of venation acropetal, overall growth ± diffuse, venation hierarchical-reticulate, secondary veins pinnate, veins (1.7-)4.1(-5.7) mm/mm2, endings free; most/all leaves with axillary buds; flowers perfect, pedicellate, ± haplomorphic, parts spiral [esp. the A], free, numbers unstable, development in general centripetal; P +, members each with a single trace, outer members not sharply differentiated from the others, not enclosing the floral bud; A many, filament not sharply distinguished from anther, stout, broad, with a single trace, anther introrse, tetrasporangiate, sporangia in two groups of two [dithecal], ± embedded in the filament, with at least outer secondary parietal cells dividing, each theca dehiscing longitudinally, endothecium +, endothecial cells elongated at right angles to long axis of anther; (tapetum glandular), cells binucleate; microspore mother cells in a block, microsporogenesis successive, walls developing by centripetal furrowing; pollen subspherical, tectum continuous or microperforate, ektexine columellate, endexine +, thin, compact, lamellate only in the apertural regions; nectary 0; carpels present, superior, free, several, ascidiate, with postgenital occlusion by secretion, stylulus short, hollow, cavity not lined by distinct epidermal layer, stigma ± decurrent, carinal, dry [not secretory]; ovules few [?1]/carpel, marginal, anatropous, bitegmic, micropyle endostomal, outer integument 2-3 cells across, often largely subdermal in origin, inner integument 2-3 cells across, often dermal in origin, parietal tissue 1-3 cells across [crassinucellate], nucellar cap?; megasporocyte single, hypodermal, functional megaspore, chalazal, lacking cuticle; female gametophyte four-celled [one module, nucleus of egg cell sister to one of the polar nuclei]; supra-stylar extra-gynoecial compitum +; ovule not increasing in size between pollination and fertilization; pollen grains landing on stigma, bicellular at dispersal, mature male gametophyte tricellular, germinating in less than 3 hours, pollination siphonogamous, tube elongated, growing between cells, growth rate (20-)80-20,000 µm/hour, apex of pectins, wall with callose, lumen with callose plugs, penetration of ovules via micropyle [porogamous], whole process takes ca 18 hours, distance to first ovule 1.1-2.1 mm; male gametes lacking cell walls, flagellae 0, double fertilization +, ovules aborting unless fertilized; P deciduous in fruit; seed exotestal, much larger than ovule at time of fertilization; endosperm diploid, cellular, heteropolar [micropylar and chalazal domains develop differently, first division oblique, micropylar end initially with a single large cell, divisions uniseriate, chalazal cell smaller, divisions in several planes], copious, oily and/or proteinaceous; dark reversal Pfr -> Pr; Arabidopsis-type telomeres [(TTTAGGG)n]; 2C genome size 1-8.2 pg [1 pg = 109 base pairs], whole nuclear genome duplication [epsilon duplication]; protoplasm dessication tolerant [plant poikilohydric]; ndhB gene 21 codons enlarged at the 5' end, single copy of LEAFY and RPB2 gene, knox genes extensively duplicated [A1-A4], AP1/FUL gene, paleo AP3 and PI genes [paralogous B-class genes] +, with "DEAER" motif, SEP3/LOFSEP and three copies of the PHY gene, [PHYB [PHYA + PHYC]].
[NYMPHAEALES [AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]]: wood fibres +; axial parenchyma diffuse or diffuse-in-aggregates; pollen monosulcate [anasulcate], tectum reticulate-perforate [here?]; ?genome duplication; "DEAER" motif in AP3 and PI genes lost, gaps in these genes.
[AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]: vessel elements with scalariform perforation plates in primary xylem; essential oils in specialized cells [lamina and P ± pellucid-punctate]; tension wood +; tectum reticulate; anther wall with outer secondary parietal cell layer dividing; carpels plicate; nucellar cap + [character lost where in eudicots?]; 12BP [4 amino acids] deletion in P1 gene.
[[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]] / MESANGIOSPERMAE: benzylisoquinoline alkaloids +; sesquiterpene synthase subfamily a [TPS-a] [?level], polyacetate derived anthraquinones + [?level]; outer epidermal walls of root elongation zone with cellulose fibrils oriented transverse to root axis; P more or less whorled, 3-merous [possible position]; pollen tube growth intra-gynoecial; embryo sac bipolar, 8 nucleate, antipodal cells persisting; endosperm triploid.
[MONOCOTS [CERATOPHYLLALES + EUDICOTS]]: (extra-floral nectaries +); (veins in lamina often 7-17 mm/mm2 or more [mean for eudicots 8.0]); (stamens opposite [two whorls of] P); (pollen tube growth fast).
[CERATOPHYLLALES + EUDICOTS]: ethereal oils 0.
EUDICOTS: (Myricetin, delphinidin +), asarone 0 [unknown in some groups, + in some asterids]; root epidermis derived from root cap [?Buxaceae, etc.]; (vessel elements with simple perforation plates in primary xylem); nodes 3:3; stomata anomocytic; flowers (dimerous), cyclic; K/outer P members with three traces, ("C" +, with a single trace); A few, (polyandry widespread, initial primordia 5, 10, or ring, ± centrifugal), filaments fairly slender, anthers basifixed; microsporogenesis simultaneous, pollen tricolpate, apertures in pairs at six points of the young tetrad [Fischer's rule], cleavage centripetal, wall with endexine; G with complete postgenital fusion, stylulus/style solid [?here]; seed coat?
[PROTEALES [TROCHODENDRALES [BUXALES + CORE EUDICOTS]]]: (axial/receptacular nectary +).
[TROCHODENDRALES [BUXALES + CORE EUDICOTS]]: benzylisoquinoline alkaloids 0; euAP3 + TM6 genes [duplication of paleoAP3 gene: B class], mitochondrial rps2 gene lost.
[BUXALES + CORE EUDICOTS]: ?
CORE EUDICOTS / GUNNERIDAE: (ellagic and gallic acids +); leaf margins serrate; compitum + [one place]; micropyle?; whole nuclear genome duplication [palaeohexaploidy, gamma triplication], PI-dB motif +, small deletion in the 18S ribosomal DNA common.
[ROSIDS ET AL. + ASTERIDS ET AL.] / PENTAPETALAE: root apical meristem closed; (cyanogenesis also via [iso]leucine, valine and phenylalanine pathways); flowers rather stereotyped: 5-merous, parts whorled; P = calyx + corolla, the calyx enclosing the flower in bud, sepals with three or more traces, petals with a single trace; stamens = 2x K/C, in two whorls, internal/adaxial to the corolla whorl, alternating, (numerous, but then usually fasciculate and/or centrifugal); pollen tricolporate; G , G  also common, when [G 2], carpels superposed, compitum +, placentation axile, style +, stigma not decurrent; endosperm nuclear; fruit dry, dehiscent, loculicidal [when a capsule]; RNase-based gametophytic incompatibility system present; floral nectaries with CRABSCLAW expression.
[DILLENIALES [SAXIFRAGALES [VITALES + ROSIDS s. str.]]]: stipules + [usually apparently inserted on the stem].
[SAXIFRAGALES [VITALES + ROSIDS]] / ROSANAE Takhtajan / SUPERROSIDAE: ??
[VITALES + ROSIDS] / ROSIDAE: anthers articulated [± dorsifixed, transition to filament narrow, connective thin].
ROSIDS: (mucilage cells with thickened inner periclinal walls and distinct cytoplasm); embryo long; genome duplication; chloroplast infA gene defunct, mitochondrial coxII.i3 intron 0.
ROSID I / FABIDAE / [ZYGOPHYLLALES [the COM clade + the nitrogen-fixing clade]]: endosperm scanty. Back to Main Tree
[FABALES [ROSALES [CUCURBITALES + FAGALES]]] / the nitrogen-fixing clade: (N-fixing by associated root-dwelling bacteria); tension wood +; seed exotestal.
Age. Wikström et al. (2001) dated this node to (96-)94, 89(-87) m.y., but other estimates are a little older - Moore et al. (2010: 95% highest posterior density) suggested ages of (107-)104(-100) m.y. and Bell et al. (2010) ages of (107-)99(-91) m. years. Stem-group ages for Fabaceae (the ages just mentioned) offered by Hengcheng Wang et al. (2009) and Magallón and Castillo (2009), while not much different, are based on a different internal topology, but Xue et al. (2012) suggested an age of a mere 68.6 or 62.2 m.y. for this clade, although again the topology is different from that used here. Around 96.8 or 86.3 m.y. are ages suggested by Naumann et al. (2013).
Evolution. Divergence & Distribution. See Taylor et al. (2012) for possible apomorphies of the whole clade.
Ecology & Physiology. The nitrogen-fixing clade is the clade in which there have been a number of associations between bacteria and plant developed the result of which is the evolution of nitrogen fixation. There have been at least six independent establishments of symbioses with Frankia, a gram-positive actinomycete, and at least two more with rhizobia (e.g. Swensen 1996; Clawson et al. 2004; Santi et al. 2013). Nitrogen-fixing plants are usually not members of closed lowland tropical rainforest communities, often growing in more open vegetation, even in early successional communities. Found in both tropical and temperate regions of the world, they are very important in the global nitrogen cycle.
The ability to fix nitrogen is uncommon elsewhere in seed plants, although nitrogen-fixing blue-green algae are associated with Gunneraceae and Cycadales. In vitro nitrogen fixation by Azotobacteria vinelandii endophytic in Mammillaria has been recorded (Lopez et al. 2011), and Burkholderia, a genus which can fix nitrogen in Fabaceae, forms associations with some Primulaceae-Myrsinoideae and Rubiaceae, and may even fix nitrogen in sugar cane (de Carvalho et al. 2011).
N-fixing taxa may also form root clusters of varying morphologies, and in some cases these have been shown to facilitate phosphorus uptake in P-poor soils (Lambers et al. 2006, 2012b). Species forming ectomycorrhizal associations are also common in the N-fixing clade, and this association has evolved at least seven times, but apparently not in Cucurbitales. Plants with ectomycorrhizae do not fix nitrogen.
Bacterial/Fungal Associations. Jeong et al. (1999) and Clawson et al. (2004) compared phylogenetic relationships within Frankia with those of its hosts. However, Clawson et al. (2004) suggested that all three clades of Frankia that they recognised might have diverged before the evolution of the angiosperms, while Jeong et al. (1999) thought that the Frankia clades had diverged more recently than the plant clades, being about one third the ages of the latter. They estimated these latter ages to be extraordinarily old, thus the [Rosales [Fagales + Cucurbitales]] clade was estimated to be 429-199 m.y.o. (Jeong et al. 1999). For the considerable gene/genome divergence within Frankia, see Normand et al. (2006).
Intercellular penetration of the root epidermis by Frankia may be the plesiomorphic route of infection, occurring in both Rosales and perhaps in Cucurbitales; in Fagales infection is through root hairs (Clawson et al. 2004; c.f. Santi et al. 2013). However, given the absence of strong phylogenetic structure in the group, details of how infection patterns map on to phylogeny are unclear (see also Soltis et al. 2005a). The situation is yet more complex, with a considerable diversity of bacteria involved in nitrogen fixation in Fabaceae alone. In Mimosa and some Faboideae, at least, ß-proteobacteria like Burkholderia phymatum and Cupriavidus form nodules that fix nitrogen. The α-proteobacteria, rhizobia, that form nodules in other Fabaceae occur in four separate clades, over a dozen "species" being involved (J. J. Doyle 1998; Moulin et al. 2001; Sprent 2002; Elliott et al. 2007; Bontemps et al. 2010). Rhizobia themselves can fix nitrogen only when in association with their host, and one of the components of the cofactor of the nitrogenase which actually fixes the nitrogen comes from the host legume (Hakoyama et al. 2009). Haemoglobin is intimately involved in helping preserve the largely oxygen-free micro-environment the bacteria need for nitrogen fixation; a variety of haemoglobins are involved, including haemoglobin synthesized by Frankia (Vessey et al. 2004).
Although there is considerable variation in nodule morphology, this does not correlate with bacterium type. In general in Fabaceae the nodules arise from the cortex and have peripheral vascular tissue with bacterial infected cells in the center; they are perhaps shoot-like structures (Hirsch & Larue 1997; Franche et al. 1998; Couzigou et al. 2012). In all other nodules, whether associated with Frankia or rhizobia, the nodules are modified lateral roots, although they lack a root cap - the vascular tissue is central, initiation of the nodule is pericyclic, and it is the cortical cells that contain bacteria (Gualtieri & Bisseling 2000; Raven & Edwards 2001; Vessey et al. 2004). However, recent work clearly shows that nodule origination in Faboideae occurs where lateral roots develop, although cortical cells may also be involved (op den Camp et al. 2011). Indeed, in nodule development in Faboideae there seems to have been co-option of genes originally involved in lateral root origination after a genome duplication event ca 54 m.y.a. (op den Camp et al. 2011). Since N-fixing clades such as Chamaecrista lack this duplication (Cannon et al. 2010), nodules presumably form in a different way there.
There is a relatively small plasmid-born "symbiosis island" that can be exchanged as a unit among bacteria and that enables nodulation to develop, although not all nodulation genes occur on the island (Sullivan & Ronson 1998; J. J. Doyle 1998). Particular legumes may select particular bacterial variants for nodulation, yet all the bacteria may have similar symbiosis islands (Parker 2012).
Nitrogen fixation in this group of four orders is a classic example of a "tendency" or a predisposition (Vessey et al. 2004), and the possible molecular reasons for the restriction of these diverse bacterial associations to the N-fixing clade are being dissected. A number of the genes involved in the establishment of both the actinomycete and Rhizobium symbiosis are the same as those involved in establishing vesicular-arbuscular mycorrhizal associations, the "SYM" (symbiosis) pathway being involved in all (Parniske 2008; Bonfante & Genre 2010; Hocher et al. 2011). One of these genes, the symbiosis receptor kinase gene, exists in a particularly distinctive form in the N-fixing clade - and also in Tropaeolum, but not rice, tomato or poppy. This gene in the latter genera rescued mycorrhizal formation in defective forms of the gene in Fabaceae, but not nodule formation, whereas the Tropaeolum gene restored the ability to form nodules (Markmann et al. 2008; see also Chen et al. 2007, 2009; Gherbi et al. 2008; Yano et al. 2008; Markmann & Parniske 2009). There are also connections betwen the signalling genes involved in arbuscular mycorrhizae symbioses and rhizobial Nod factors involved in nodulation in legumes (Maillet et al. 2010; Op den Camp et al. 2010; Streng et al. 2011; Roberts et al. 2012), the rhizobia acquiring the nod gene by horizontal transfer (Suominen et al. 2001). Although Nod factors do not occur in actinorhizal associations, there is notable similarity at the transcriptional level in the genes involved in the establishment of endosymbioses in Casuarina, Alnus (both associates of actinorhiza), and legumes (Hocher et al. 2011).
Plant-Animal Interactions. There are associations of particular groups of butterflies and plants (as food sources for caterpillars) within Fabales and Rosales in particular (Ackery 1988, 1991). Indeed, it has been suggested, as by Scott (1985) and Janz and Nylin (1998; see also Braby & Trueman 2006) that the ancestral food plant for larvae of butterflies as a whole may perhaps have been somewhere in the N-ixing clade or the malvids or their (immediate) ancestors (Nylin et al. 2014), however, caterpillars are common in the latter only on Fabaceae, a fairly young, mostly Tertiary group (see below); stem Fabales are rather older (see above). Malvales are another possibility (Ackery 1991), as are Rosids as a whole (e.g. Powell 1980; Berenbaum & Passoa 1999).
Chemistry, Morphology, etc. Whether or not the presence of stipules is plesiomorphic in the clade depends in part on its phylogeny, but there is clearly a variety of structures borne at the node - and nodal anatomy is also variable (see below: de Aguiar-Dias et al. 2011).
Phylogeny. For the limits of the N-fixing clade, a rather unexpected group, see Chase et al. (1993, 1999), Savolainen et al. (1997), Soltis et al. (1995b, 1997, 1998), and Swensen (1996). Although it was not recovered by some analyses of the complete chloroplast genome (Bausher et al. 2006), the poor sampling - no other fabids/rosid I taxa were included - may well be reponsible; the nitrogen-fixing clade was also found not to be monophyletic in Duarte et al. (2010) or in the genome-level analysis of Burleigh et al. (2011). The clade had little support in the mitochondrial matR analysis of Zhu et al. (2007), but support was much strengthened when two chloroplast genes were added; it was also monophyletic in the mitochondrial analysis of Qiu et al. (2010). For further discussion of the relationships of the N-fixing clade, an ancestor of which was possibly involved in an ancient hybridization, see the Zygophyllales page.
Relationships within the clade are still somewhat unclear (e.g. Qiu et al. 2010; Xue et al. 2012), and Zhu et al. (2007) could not even recover a monophyletic Rosales using the mitochondrial matR gene; the other three orders were, however, all strongly supported. Sytsma et al. (2002) recovered a topology [Cucurbitales [Fabales [Fagales + Rosales]]], while in Zhu et al. (2007: four genes) and Lee et al (2011: focus on nuclear genome) relationships were [Fab [C [Fag + R]]], albeit there was little support for the topologies found (see also Bell et al. 20100. However, Ravi et al. (2007) examining data sets including 61 protein-coding genes (for only three orders) and just four genes (Fagales included) found good support for [Fab + R] and some support for the broader grouping [C [Fag [Fab + R]]]. However, apart from Fabales (three Fabaceae-Faboideae included), the other orders were represented by single exemplars. A [Fab + R] clade was also obtained by Jansen et al. (2007) and Moore et al. (2007), but no Fagales were included. In other analyses there is some support for a [C + Fag] clade (see Chase et al. 1993; Setoguchi et al. 1999; Schwarzbach & Ricklefs 2000; Soltis et al. 2000, 2003a; Zhang et al. 2006). However, the support for the topology in the Summary Tree is quite strong (Jeong et al. 1999: no Fabaceae included; Moore et al. 2008, 2011; Hengcheng Wang et al. 2009; Soltis et al. 2011), but confirmation after e.g. increased taxon sampling would be comforting.
FABALES Bromhead Main Tree.
Ellagic acid 0; vessel elements with simple perforation plates; wood often fluorescing; nodes?; styloids +; K initiation helical; C clawed; embryo green. - 4 families, 754 genera, 20140 species.
Age. Wikström et al. (2001) date crown-group Fabales to (83-)79, 74(-71) m.y.a.; other estimates are (90-)87(-84) or (75-)72(-69) m.y. (two penalized likelihood dates), Bayesian relaxed clock estimates being slightly older, to 100 m.y. (Hengcheng Wang et al. 2009).
Note: Possible apomorphies are in bold. However, the actual level at which many of these features, particularly the more cryptic ones, should be assigned is unclear. This is partly because many characters show considerable homoplasy, in addition, basic information for all too many is very incomplete, frequently coming from taxa well embedded in the clade of interest and so making the position of any putative apomorphy uncertain. Then there is the not-so-trivial issue of how ancestral states are reconstructed (see above).
Evolution. Divergence & Distribution. Fabales contain ca 9.6% eudicot diversity (Magallón et al. 1999), of which the bulk is made up of Fabaceae.
Bello et al. (2012) suggested a number of apomorphies for Fabales; Krameria was used as the outgroup because people in the past had suggested similarities between it and Polygalaceae and most of the apomorphies listed are likely to be plesiomorphies. Despite the floral differences between Polygalaceae and Fabaceae, there are some developmental similarities between them (Prenner 2004d), however, the keel flowers in the two may have arisen independently (Bello et al. 2012). Indeeed, given the uncertainty over the relationships between the four families, optimisation of characters is a particularly fraught enterprise here.
Ecology & Physiology. About a quarter of all records of extra-floral nectaries come from members of this clade (Weber & Keeler 2013).
Chemistry, Morphology, etc. The distribution of a number of features may be of systematic significance in Fabales, but sampling is poor. Variation in nodal anatomy within Surianaceae is correlated with presence/absence of stipules. Although styloids, along with druses, are reported from Surianaceae, Quillajaceae and Fabaceae, details of their distribution within Fabaceae are unclear; they are certainly quite common in Faboideae (Lersten & Horner 2005), apparently less so in the rest of the family. The rpl22 gene is in the nucleus in Polygalaceae and Fabaceae (i.e. it is absent from the chloroplast), but other members of the order have not been studied and its presence in other angiosperms is sporadic (J. J. Doyle et al. 1995). Pollen grains of Quillajaceae and some Surianaceae have exine protruding at the apertures, and these and some Fabaceae-Cercideae (although perhaps derived within that group?) have striate pollen (Banks et al. 2003; Claxton et al. 2005); these features are unlikely to be high-level apomorphies. It would be nice to know if Surianaceae or Quillajaceae had starchy endosperm, and more details of their chemistry are needed. Many Fabaceae-Faboideae have lost the rps16 gene, and it is also absent from Polygala (Downie & Palmer 1992: again, sampling).
Phylogeny. Fabales as circumscribed here were rather unexpected, but they are quite strongly supported (Morgan et al. 1994; Källersjö et al. 1998, etc.). Although Hilu et al. (2003) found Larrea (Zygophyllaceae) to be weakly associated with Fabaceae, they were the only Fabales included in their rbcL analysis.
Within Fabales, Persson (2001) suggested the relationships [Polygalaceae [Surianaceae [Quillajaceae + Fabaceae]]], but there was little support for this (see the tree in versions 1-6). Forest et al. (2002, see also Qiu et al. 2010) found weak support for the topology of the tree below, and Banks et al. (2008) also found strong support for the relationship [Quillajaceae [the rest]]. However, Wojciechowski et al. (2004: ?sampling) suggested the possibility of a [Surianaceae + Quillajaceae] grouping. The unrooted topology in Bruneau et al. (2008a) is [Polygalaceae [Quillajaceae + Surianaceae] Fabaceae]. Bello et al. (2009) in a careful analysis of matK and rbcL data, preferred the relationships [Polygalaceae [Fabaceae [Surianaceae + Quillajaceae]]] obtained in a maximum parsimony analysis, however, support was poor, and if anything was still poorer for any relationships obtained in Bayesian analyses of the same data. Wang et al. (2009) did not obtain well supported relationships in this clade in their twelve-gene analysis of the rosids, while in a megaphylogeny of angiosperms Smith et al. (2011) found some support for a clade [Quillajaceae + Fabaceae]. Relationships remained unclear in the study by Soltis et al. (2011). Bello returned to the problem and included morphological data with a two-gene data set. In various analyses [Surianaceae + Quillajaceae] were usually at least moderately supported, but support for Fabaceae and Polygalaceae as being successively sister to that pair was weak (Bello et al. 2012). The bottom line: The topology of the tree used here may be quite wrong!
Includes Fabaceae, Polygalaceae, Quillajaceae, Surianaceae.
Synonymy: Caesalpiniales Martius, Cassiales Link, Mimosales Link, Polygalales Berchtold & J. Presl, Quillajales Doweld, Surianales Doweld - Fabanae Reveal, Polygalanae Doweld - Polygalopsida Endlicher
QUILLAJACEAE D. Don Back to Fabales
Small evergreen tree; saponins, proanthodelphinidin, flavone C-glycosides +; cork cambium ?deep-seated; storying?; styloids in phloem +; nodes 1:3; petiole bundles arcuate, pericyclic fibres 0; mucilage cells +; hairs warty; leaves spiral, blade vernation conduplicate, margins toothed [hydathodal?], (entire), stipules petiolar; inflorescence terminal, cymose; hypanthium +; K valvate, nectary on lower half of K/hypanthium, C contorted, spathulate; A unidirectional in initiation, 5A opposite sepals above nectary + 5A opposite petals below nectary; pollen striate; G , deeply longitudinally ridged, opposite K, stigmatic zone elongated down short style branches; ovules several/carpel, apotropous to pleurotropous, in two marginal rows, micropyle?, outer integument ?3 cells across, inner integument?; fruit strongly asymmetrically lobed, follicular, opening down both surfaces of the lobes, K moderately accrescent; seeds winged; testa with 3 outer layers thickened, sclerotic, tegmen disintegrating; endosperm type?, cotyledons investing radicle, conduplicate; n = 14, 17.
1/3. Temperate South America (map: from Donoso Z. 1994; Culham 2007). [Photo - Flower, Fruit.]
Chemistry, Morphology, etc. The leaves are amphistomatous. The flowers of Quillajaceae, with the distinctive arrangement of nectary and androecium, may be interpreted as having a hypanthium. Androecial development is unidirectional and is rather like that of Fabaceae (Bello et al. 2007/8); the carpels are definitely connate axially, but are largely free laterally, c.f. earlier versions of this site. There appear to be only three traces to each carpel, although Sterling (1969) noted that there were also "intermediate" bundles. Robertson (1974) noted that n = 17. Embryologically the family is poorly known.
See also Péchoutre (1902, as Rosaceae) for seed morphology, Hegnauer (1973, 1990, as Rosaceae) for chemistry, Sterling (1969) and Kania (1973) for gynoecial morphology, Lersten and Horner (2005) for vegetative anatomy, Kubitzki (2006b) for a general account, and Marchiori et al. (2009) for wood anatomy (intercellular canals, included phloem). Additional data from: Aronson 7897 (anatomy, embryo).
Previous Relationships. Quillaja was included in Rosaceae-Quillajoideae (Takhtajan 1997) or, more usually, in Spiraeaoideae, e.g. as Quillajeae (Robertson 1974). It is indeed superficially quite similar to the South American Kageneckia (Spiraeaoideae), but wood anatomical data, etc., suggest that it should be removed from Rosaceae (Lotova & Timonin 1999; c.f. Zhang 1992).
[Fabaceae [Surianaceae + Polygalaceae]]: suspensor persistent, also connected to wall of embryo sac [?Surianaceae].
Age. Crown group ages of this clade are (82-)79, 74(-71) m.y. (Wikström et al. 2001) or ca 70.6 m.y. (Naumann et al. 2013).
FABACEAE Lindley, nom. cons.//LEGUMINOSAE Jussieu, nom. cons. et nom. alt. Back to Fabales
Trees to annual herbs; (coumarins/furanocoumarins +), (cyanogenic glucosides +), lectins [haemagglutinins] and gums esp. in seeds, 5-deoxyflavonoids, C-glycosylflavonoids, pinitol [cyclitol] +; (ectomycorrhizae scattered); cork also in outer cortex; cambium storied; secretory cells common, sieve tube plastids with protein crystals (and/or starch, or simply starch); nodes 3:3; cuticle wax platelets as rosettes; stomata various; branching from previous flush; colleters +, hairs often uniseriate (mesifixed); leaves compound, apex of petiole and petiolules pulvinate, leaflets stipellate or not, opposite (alternate), vernation conduplicate, (glandular-punctate), (margins lobed, toothed), (secondary veins palmate); inflorescence racemose; flowers monosymmetric, inverted [median sepal abaxial], (3-)5(-6)-merous, floral developmental sequence K-G-C-outer whorl A-inner whorl A [G initiation/development much advanced], hypanthium +; C with adaxial-median member internal [descending cochleate], (adaxial-median C with patterning/different in colour from the other C); A unidirectional in initiation, (2-)10(-many); tapetal cells bi(multi)nucleate; G 1, stipitate, stylulus long, (hollow), stigma expanded or not, wet; ovules several/carpel, one-ranked, micropyle zig-zag, outer integument 2-10 cells across, inner integument 2-3 cells across, parietal tissue to 5 cells across, nucellar cap ca 3 cells across, vascular bundle in antiraphe, funicle long; (megaspore mother cells several), chalazal embryo haustorium +; fruit follicular, dehiscing abaxially also; seed symmetric, pleurogram + [area of cells with a deep-seated linea lucida] (0), linea fissura + [fine line delimiting pleurogram], ± circular/oval [closed; ?level]; exotesta palisade, linea lucida separating much thickened outer anticlinal walls from the thinner inner walls, mesotesta of stellate cells, (seed coat undistinguished), tegmen crushed; (thick-walled endosperm with galactomannans [Schleimendosperm]), chalazal endosperm haustoria + [?level]; embryo ± straight, cotyledons investing radicle; rpl22 gene transferred from chloroplast to nucleus, rps19 pseudogene present.
745/19560 - discussed in eight or so groups below. World-wide.
Age. Wikström et al. (2001, 2004) date the crown group to (71-)68(-65) or (59-)56(-53) m.y.a.; Bruneau et al. (2008a, b; slightly younger estimates in Bello et al. 2009) thought that Fabaceae began diversifying in the Palaeocene ca 60-64 m.y. ago. Crown Fabaceae are dated to ca 59 m.y.a. by Lavin et al. (2005) and (77-)63, 61(-47) m.y. by Bell et al. (2010). These ages assume that Cercideae are sister to all other Fabaceae.
A Gondwanan age for Amherstieae (= Detarieae), and so a proportionally older age for the family as a whole, suggested because of their amphiatlantic distribution and common possession of ectomycorrhizae (Henkel et al. 2002), seems unlikely.
Trees or shrubs to lianes climbing by branch tendrils; (distinctive secondary thickening), (intraxylary phloem/bicollateral vascular bundles +); leaves apparently simple, bilobed or not (bifoliolate), with single pulvinus; pollen (striate), (in tetrads), (0-5 aperturate), (pororate), (surface various); (funicle short); (seeds asymmetric); n = 7, (13), 14, etc.
13/265: Bauhinia (250). Pantropical (temperate) (map: from Meusel et al. 1965; Sales & Hedge 1996; Trop. Afr. Fl. Pl. Ecol. Distr. 3. 2008). [Photo - Bauhinia, Cercis, © D. Kimbler.]
Age. The age of crown-group Cercideae is estimated at ca 34 m.y. (Lavin et al. 2005) or ca 62.7 m.y. (Meng et al. 2014); see Meng et al. (2014) for a list of fossils of Bauhinia.
Synonymy: Bauhiniaceae Martynov
Leaves once-compound; K 4, petal-like, adaxial-median C external; A 4, opposite K, connate, anthers porose; pollen asymmetric, ectoaperture encircling the equator, with two endoapertures; G initiation not advanced relative to that of other organs [development "normal"].
1/1: Duparquetia orchidacea. Tropical W. Africa.
1c. Detarieae de Candolle
Plant ectomycorrhizal; (resins +, with bicyclic diterpenes); leaf phloem transfer cells +; leaflets with crater-like glands on the abaxial surface, stipules caducous, intrapetiolar; inflorescences branched; (bracteoles well developed, ± surrounding floral apex, imbricate, caducous); K petal-like (not), C5 (->0 [adaxial C the last to go]); A with overlap of initiation of the two whorls, (from ring meristem), some connate or not; (pollen striate); G adnate to side of hypanthium (not), style bent abaxially; (seed arillate); endosperm 0, cotyledons with thick-walled cells [amyloid, xyloglucans]; x = 12.
82-84/750: Cynometra (85), Macrolobium (75), Crudia (550, Copaifera (35). Tropical.
Age. The crown age of this clade is ca 29.2 m.y. (Lavin et al. 2005).
Synonymy: Detariaceae J. Hess
1d. Dialieae Nakai
Inflorescences cymose; K (3-4), C (0-4); A 2-5(-10); (G 2).
14/56: Dialium (28). Tropical.
[["Caesalpinioideae" + Mimosoideae] Faboideae]: (non-protein amino acids, esp. in seeds, +); vestured pits + (0); Leaves equal- or odd-pinnately compound (palmate, simple); (fruit a drupe, samara, schizocarp, etc.); (seed arillate).
Age. This node has been dated to (62-)59, 53(-50) or (36-)34(-31) m.y.a. (Wikström et al. 2001), (67-)50, 49(-30) m.y. (Bell et al. 2010), or ca 55 m.y. (Lavin et al. 2005; not very dissimilar ages in Bouchenak-Khelladi et al. 2010b).
["Caesalpinioideae" + Mimosoideae]: (extrafloral nectaries +).
2. "Caesalpinioideae" de Candolle
Shrubs or trees (herbs); (N-fixing +, rhizobia remain in infection threads - Chamaecrista); non-protein amino acids +; sieve tube plastids also with fibres; leaves bicompound or not; (inflorescence cymose - Chamaecrista); (G adnate to side of hypanthium); ovules usu. campylotropous [up a level?], outer integument with vascular strand; (aril 0), funicle long and thin to stout and thick, (pleurogram +), (linea fissura 0, several); (cotyledons with thick-walled cells [amyloid, xyloglucans]).
160[list]/1930: Senna (295-350), Chamaecrista (265). Tachigali (60). Predominantly tropical, esp. Africa and America. [Photos - Collection]
Synonymy: Caesalpiniaceae R. Brown, Cassiaceae Vest, Ceratoniaceae Link[?]
3. Mimosoideae de Candolle
Shrubs or trees (herbs); N-fixing common; albizziine [non-protein amino acid] +, exudates mostly gums; sieve tube plastids also with fibres; (septate fibres +; aliform axial parenchyma); rays usu. 20< cells high; leaves often bicompound, petiolar extrafloral nectaries common; inflorescences ± capitate, flowers opening together, organ initiation in all flowers of the one head beginning simultaneously; flowers rather small, polysymmetric, bracteoles 0, hypanthium often 0; K connate, median sepal adaxial, valvate (imbricate; much reduced), C enclosing the flower in bud, connate (free), valvate, not clawed, not patterned; A often connate, (many, from ring primordium); tapetal cells uninucleate; pollen polyads common; (G 1< [Inga]; if 5, opposite K - [Archidendron lucyi]), stigma (dry - one record), cup-shaped, (peltate); (nucellus apex exposed); seed (arillate), funicle long, thin; testa with vascular strand, linea fissura U-shaped [open], (0); suspensor vestigial at cotyledon stage, detached from wall of embryo sac.
82[list]/3335: Acacia s. str. (1030), Mimosa (480), Inga (350), Vachellia (161), Calliandra (150), Senegalia (85), Prosopis (45), Pithecellobium (40). Esp. tropical and warm temperate, esp. Africa and America (map: from Vester 1940; Maslin et al. 2003; Trop. Afr. Fl. Pl. Ecol. Distr. 3. 2008a). [Photos - Collection.]
Age. Crown group Mimosoideae s. str. have been dated to (49.5-)42.4, 40.5(-31.3) m.y. (Lavin et al. 2005: inc. Pentaclethra; ages in Bouchenak-Khelladi et al. (2010b) are (61-)59.5(-58) m.y., while (62.7-)51.4(-15.0) m.y. is the estimate in Miller et al. (2013).
Synonymy: Acaciaceae E. Meyer, Mimosaceae R. Brown
4. Faboideae Rudd / Papilionoideae Jussieu, nom. alt.
Isoflavonoids [pterocarpans and isoflavans], prenylated flavonoids, indolizidine, and quinolizidine alkaloids +, exudates mostly gums; sieve tubes with spindle-shaped non-dispersive protein bodies [forisomes]; (cork cambium deep seated); leaves once compound; ?tapetal cells; (pollen porate); stigma semi-dry; seed pleurogram 0, linea fissura 0.
Age. Crown group Faboideae may be about 59 m.y.o. (Lavin et al. 2005), but this age is rather sensitive to that of Fabaceae as a whole.
Trees, shrubs; plant N-fixing; stipels + (0); hypanthium 0; K completely connate, opening irregularly, C 1 (0, 2); A many, from ring meristem, development centripetal or centrifugal, dimorphic; nectary 0; (G 2-4), long-stipitate; ovules anatropous, micropyle zig-zag, outer integument 6-8 cells across, inner integument 5-6 cells across, ?parietal tissue; seed usu. arillate; coat thin, cracking; embryo straight; n = 14.
8/213: Swartzia (180), Ateleia (20). Mostly Central and South America; Bobgunnia Africa (Map: from Cowan 1967).
Age. The age for a crown group around here is 48.9±2.8 m.y. (Lavin et al. 2005: inc. Ateleia, Bobgunnia).
Synonymy: Swartziaceae Bartling
[Angylocalyceae [Dipterygeae + Amburaneae]]: ?
K/hypanthium well developed, petals thick; stamens exserted.
5/21. Tropical, Castanospermum in Australia.
Two adaxial calyx lobes very much expanded, petal-like (green), corolla often papilionoid; secretory cavities in apical appendices of K and C (and elsewhere in the flower).
Plant resiniferous; leaflets punctate.
7/29. Mostly Neotropics (Africa).
1/18. East Asias, Western and eastern North America.
4. 50 KB inversion clade / The Rest.
Herbs, vines (lianes, trees, shrubs); (N-fixing 0); (ectomycorrhizae +); (rotenone +), (quinolizidine alkaloids - Genisteae, Sophoreae, etc.), (pyrrolizidine alkaloids - Crotalarieae); (nodes 1:1); (styloids +); (leaves 2+ compound); palmate), (pulvini 0); hypanthium usu. 0; K, C, A with unidirectional [abaxial to adaxial] initiation; K connate, adaxial-median C external [= ascending cochleate], 2 abaxial C connate; A connate [e.g. 9 + 1], (not); tapetal cells uninucleate; (pollen porate); (stigma wet - Crotalaria); ovules usu. campylotropous, (endothelium +), (integumentary endothelium +), antiraphe bundle (+ Canavalia, Sophora), funicle short; seed asymmetric, not arillate; testa (multiplicative), hour-glass cells + [below palisade exotesta], raphe shorter than the antiraphe, hilum with a hilar groove, with tracheid bar [group of tracheids just below surface of hilum] and recurrent vascular bundles, counter palisade +; cotyledons accumbent, not investing radicle, cotyledon areole +, (xyloglucans +, starch in embryo), (endosperm 0), embryo curved, radicle long; 50 kb inversion in trnL intron in chloroplast LSC, (rps16 gene absent; ORF184 absent), duplication of CYC gene.
Non-protein amino acid accumulating clade: alkaloids 0; non-protein amino acid accumulation [e.g. canavanine]; whole genome duplication?
IRLC clade: one much-enlarged pleiomorphic bacterium in symbiosome; leaves lack pulvini, FLO/LFY genes expressed also in the leaf; CA primordia +; A initiation bidirectional, overlap in the timing of C, A, and G initiation; (stigma wet); chloroplast inverted repeat lost.
475[list]/13715 (abbreviations - BAPH = baphioids, DAL = dalbergioids s.l., GEN = genistoids, IRLC = Inverted Repeat Loss Clade, MILL = Indigofereae + millettioids, MIRB = mirbelioids, ROB = robinioids): Astragalus (2910: IRLC), Indigofera (700: aff. MILL, mesifixed hairs), Crotalaria (700: GEN), Mirbelia s.l. (450: MIRB), Tephrosia (350: MILL), Desmodium (300: MILL), Aspalathus (300: GEN), Oxytropis (300: IRLC), Lupinus (270: IRLC), Adesmia (240-425: DAL), Trifolium (240: IRLC), Rhynchosia (230: MILL), Aeschyomene (160: DALB), Hedysarum (160: IRLC), Lathyrus (160: IRLC), Vicia (160: IRLC), Dalea (150: DALB), Eriosema (150: MILL), Millettia (150: MILL), Daviesia (135: MIRB), Machaerium (130: DALB), Onobrychis (130: IRLC), Ormosia (130: unplaced), Lotus (inc. Coronilla: 125: ROB), Erythrina (110: MILL), Gastrolobium s.l. (110: MIRB), Mucuna (105: MILL), Lonchocarpus (100: MILL), Lotononis (100: GEN), Pultenaea (100: MIRB), Vigna (90+: MILL), Genista (90: GEN), Medicago (87: IRLC), Swainsonia (85: IRLC), Caragana (75: IRLC), Jacksonia (75: MIRB), Ononis (75: IRLC), Phaseolus (75: MILL), Zornia (75: DALB), Argyrolobium (70: GEN), Arachis (70-80: DAL), Cytisus (65: GEN), Bossiaea (60: MIRB), Canavalia (60: MILL), Clitoria (60: MILL), Dolichos (60: MILL), Galactia (60: MILL), Lebordea (60: GEN), Sesbania (60: ROB), Brongniartia (55: GEN), Derris (55: MILL), Lessertia (50: IRLC), Psoralea (50: MILL), Sophora (50: GEN), Caragana (50: IRLC). Esp. (warm) temperate, but world-wide (map: from Vester 1940; Meusel et al. 1965; Hultén 1971; Trop. Afr. Fl. Pl. Ecol. Distr. 3. 2008a, 4. 2008b). [Photo - Flower, Fruit, Collection.]
Synonymy: Aspalathaceae Martynov, Astragalaceae Berchtold & J. Presl, Ciceraceae W. Steele, Coronillaceae Martynov, Cytisaceae Berchtold & J. Presl, Dalbergiaceae Martinov, Daleaceae Berchtold & J. Presl, Galedupaceae Martynov, Geoffroeaceae Martius, Hedysaraceae Oken, Inocarpaceae Berchtold & J. Presl, Lathyraceae Burnett, Lotaceae Oken, Papilionaceae Giseke, Phaseolaceae Martius, Robiniaceae Vest, Sophoraceae Berchtold & J. Presl, Tamarindaceae Martinov, Trifoliaceae Berchtold & J. Presl, Viciaceae Oken
Floral formula: ↑ K 5; C 5; A 10; N; G 1.
Floral formula: * K ; C ; A 10-many/[10-many]; N; G 1.
Floral formula: ↑ K 5; C 5; A 10/ + 1/; N; G 1.
Evolution. Divergence & Distribution. Fabaceae are a notably speciose clade, particularly the branches with Mimosoideae and Faboideae (Magallón & Sanderson 2001), and contain ca 9.4% of eudicots. Shoemaker et al. (2006) and Soltis et al. (2009) think, although with some hesitation, that diversification in Faboideae may be connected to a genome duplication immediately basal to the split between mirbelioids and the rest; this is the clade that is notable for the occurrence of the non-protein amino acid canavanine. This duplication has also been implicated in nodule formation in Faboideae, perhaps helping to explain nodule diversity there (Q.-G. Li et al. 2013). See also rate shifts in Smith et al. (2011) and discussion below under Ecology & Physiology.
Bruneau et al. (2008a, b) thought that the major clades in Fabaceae had separated by 58-55 m.y.a.; the crown ages of the major clades are 56-34 m.y. ago, and numerous ages for nodes throughout the family are given by Lavin et al. (2005). It is thought that diversification in Cercis began ca 35 m.y.a., and spread was from east to west - and across the Atlantic (Fritsch & Cruz 2012); see also Meng et al. (2014) for dates of clade split in Cercideae. Marazzi and Sanderson (2010) suggest an age of 53-47.5 m.y. for stem group Senna, (47-)45(-41.7) m.y. for the speciose crown group.
Diversification and distribution of Fabaceae in best thought of in terms of vicariance of biomes rather than of classic geographical areas (Lavin et al. 2004; Schrire et al. 2005). There are a number of transoceanic disjunctions within the family, but 51/59 of these are only 1-22 m.y. old (Schrire et al. 2005; Bouchenak-Khelladi et al. 2010b); the North Atlantic land bridge may have been important in the Tertiary dispersal of the family (Lavin et al. 2000). One particularly interesting connection is in Hymenaea, whose resin forms valuable amber deposits. The majority of the species are New World, but there is a single Old World species, H. verrucosa. Both the Mexican and Dominican ambers seems to have been produced by extinct species whose immediate relationships are likely to be with H. verrucosa (Poinar & Brown 2002).
Early divergence within Mimosoideae seems to have occurred in Africa (Bouchenak-Khelladi et al. 2010b). The age of the crown-group clade [Ingeae + Acacieae] is estimated at (24.5-)21(-17.2) m.y. by de Souza et al (2013), q.v. for other dates in the Calliandra area. Inga, with some 350 species, has diversified in the LTRF that it prefers only within the last 2 m.y. (Richardson et al. 2001b; Pennington et al. 2009; Dexter et al. 2010: thoughts on species limits); extinction might also cause this pattern (Crisp & Cook 2009). Estimates of the age of crown-group Acacia, some 1,000+ species, range from 26.6-3.3 m.y.a., the older age being driven by recent fossil discoveries (Miller et al. 2013, q.v. for dates of the other ex Acacia genera, etc.). González-Orozco et al. (2013) plotted the distribution of Australian Acacia (practically the whole genus) in the context of various environmental factors, and they thought that climatic variables were correlated with the largest-scale patterns; Mishler et al. (2014) looked at patterns of endemism taking into account endemism and age of clades, and found areas of paleoendemism scattered in the continent, with neoendemism particularly apparent in soutwestern Australia in particular. The very close similarity between A. koa, from Hawaii, and A. heterophylla, from Réunion Island and some 18,000 km distant, is surprising. It has been explained by movement by Austronesians of a species like A. melanoxylon from eastern Australia (Brown et al. 2012). However, given the structure of relationships - A. heterophylla is embedded in A. koa, the combined clade being sister to A. melanoxylon - long distance dispersal from Hawii to Réunion, implausible although it may seem, is more likely (Le Roux et al. 2014).
Of the 116 genera of Faboideae in clades below the non-protein accumulating acid (NPAA) clade, most (ca 70%) are small, with 10 or fewer species. However, the flowers in those clades are very diverse, many genera having other than papilionoid flowers (Cardoso et al. 2013). Within the NPAA clade, there has been much diversification of Indigofereae in succulent biomes, clades growing there tending to be geographically more restricted than those common in grassland biomes; ages of crown groups of the four clades into which species of Indigofera (aff. Millettioids) fall is ca 15.5 m.y. or less (Schrire et al. 2009). Apparent independent increases in the rate of diversification in the [Mirbelieae + Bossieae] and Podalyrieae clades (mirbelioids) may rather be the results of extinctions caused by cooling climates and increased seasonality ca 32-30 m.y.a. in the early Oligocene (Crisp & Cook 2009), and Crisp and Cook (2007) date the development of SW/SE Australian disjunctions to vicariant events caused by the development of aridity in the Nullarbor plane some 14-13 m.y.a. (other climatic events could also be implicated). On the other hand, for Schnitzler et al. (2011) diversification of the ca 128 species of Podalyrieae in the Cape Flora began ca 33 m.y.a. at the end of the Eocene and was connected with shifts in how the plants survived fires. Divergence of woody clades in the Old World phaseoloids (millettioids) (crown group age ca 28.6 m.y.a.) has been associated with Late Oligocene warmness and aridity, and of herbaceous members with tropical arid climates in the Early Miocene (H. Li et al. 2013).
Hologalegina have been dated to 56±0.9 m.y., and crown robinioids to 48.3±1 m.y. (Lavin et al. 2005). Robinieae may have been diversifying for some 30 m.y. in the neotropical seasonally dry tropical forest (Pennington et al. 2009). The IRLC clade includes ca 4,500 species or more and is dated to 39±2.4 m.y.a. (Lavin et al. 2005). Within the ILRC, the speciose Astragalus, with around 2,865 species, characterises drier areas of both hemispheres, and a number of taxa have leaf rhachis spines; it separated from Oxytropis (the latter has a beak on its keel) 16-12 m.y.a., and diversification is still more recent. In particular, radiation in the speciose aneuploid New World neoastragalus clade (ca 500 species) started ca 4.4 m.y.a. (Wojciechowski 2004), with two invasions of west South America - there are over 100 species there - timed at a mere 2.07-1.62 m.y.a. (the larger group) and 1.23-0.79 m.y.a. (the smaller group) showing very high diversification rates (Scherson et al. 2008).
Several major clades that are correlated with geography have been detected in Lupinus (Aïnouche & Bayer 1999, support not very strong; Aïnouche et al. 2004). Within one of these clades there has been a recent (ca 2.7 m.y.) Central American/Andean radiation that is now represented by over eighty species, some 56 of which grow in the páramo, the rate of diversification increasing as the genus moved into Andean South America from Central America (Moore & Donoghue 2009; see also Silvestro et al. 2011; Sklenár et al. 2011). Species of Lupinus there, and in montane North America, where there had been an earlier burst of diversification, are largely perennials (Drummond 2008; Drummond et al. 2012), the annual habit being plesiomorphous, and they show much variation in habit, etc. Perennials also diversified in eastern South America ca 6.5 m.y.a.; they are separately related to east North American annuals (Drummond et al. 2012). This South American speciation may also be connected with the movement of bumble bees from North to South America some six m.y.a. (Hughes & Eastwood 2006) - there are ca 171 species of Lupinus in South America versus ca 90 species in the whole northern hemisphere (von Hagen & Kadereit 2003). Ree et al. (2003) studied aspects of LEGCYC gene evolution in the context of variation of floral morphology in the genus.
Bello et al. (2012) suggest a couple of apomorphies for the family and for clades within it.
Ecology & Physiology. Fabaceae grow in closed lowland tropical rainforst, but they are also often members of more open vegetation, even of early successional communities, in both tropical and temperate regions of the world. Perhaps 16% of all woody species in neotropical rainforest are members of Fabaceae (Burnham & Johnson 2004), indeed, they are the most speciose family in lowland tropical rainforest and also drier forest types in both America and Africa (Gentry 1988). They make up perhaps the second most important family of lianes, both ecologically and in terms of number of species, in the New World (Gentry 1991) and are overwhelmingly the most common family in Amazonian forests in terms of numbers of species and individuals with stems 10 cm or more across, althouth they do not have a disproportionally high number of locally abundant species (ter Steege et al. 2013).
There is a substantial increase in leaf nitrogen at this node, along with a preference for less seasonality in precipitation (Cornwell et al. 2014).
Associations with nitrogen-fixing bacteria are very common (see below), and substantial amounts of nitrogen can be fixed (e.g. Batterman et al. 2013: Panama). However, the role of legumes in the nitrogen cycle of tropical forests is unclear. Some work suggests that N-fixation is facultative, and in old, relatively nutrient-rich forests, nitrogen fixation by legumes (in the example, species of Inga) decreases when compared with species growing in seasonally flooded forests and in light gaps (Barron et al. 2011); other species of Fabaceae also have low fixation rates in mature forests (Barron et al. 2011 and literature; Batterman et al. 2013). The effectiveness of nodulation is often reduced in more acid soils, although Lupinus and Mimosa in Brazil, at least, may be exceptions (Lin et al. 2012). Australia is unusual in that woody Fabaceae, especially Acacia, are notable components of most vegetation types, at least for part of the succession (Orians & Milewski 2007). It has been suggested that N-fixing tropical forest legumes may have a competitive advantage over non-nodulators as atmospheric CO2 concentration increases (Cernusak et al. 2011).
Some Fabaceae - most records are from Old World, particularly African, Detarieae - are ectomycorrhizal (ECM) (e.g. Onguene & Kuyper 2001); the ECM habit has evolved at least four times in the family (M. E. Smith et al. 2011). Estimates of the number of Detarieae involved range from 250 (Brundrett 2009) to 450 species (B. Mackinder pers. comm. viii.2012). Some 36 of the ca 82 genera included in Detarieae are reported to be at least locally dominant (e.g. Letouzey 1968; Mackinder 2005), 11 of these genera being in the rather small Macrolobieae/the Berlinia clade of only 16 genera, and of which 10 are known to be ECM (see also Wieringa & Gervais 2003). Some Detarieae are endomycorrhizal/vesicular arbuscular mycorrhizal (VAM) (see Cynometra below).
All told, Detarieae occupy ca 2.8-3.3 m km2 in the Zambezian region alone (estimated from White 1983). In Miombo forests they represent 20-90% of the trees, 30-96% of the basal area, and with biomass estimates in the range of 35-97 Mg ha-1 (Frost 1996). Detarieae like Isoberlinia and Brachystegia are very important components of the widespread deciduous Miombo forests which grow on often rather poor soils over some 2.7 million km2 of central Africa, and these forests are the centre of diversity of Brachystegia (e.g. White 1983; Högberg 1990; S. E. Smith & Read 2008 for references). Many other species, both of trees and herbs, also grow in these communities, interestingly, the trees include other ECM taxa like Monotes (Dipterocarpaceae) and Uapaca (Phyllanthaceae) (White 1983). Colophospermum mopane, an important food for elephants, dominates ca 50,000 km2 of mopane woodland (e.g. Torti et al. 2001; Mackinder 2005; Newbery et al. 2006), these, along with Miombo forests, form a major part of the Zambezian Region. Isoberlinia is a major component of Sudanian Woodland (White 1983) which forms an interrupted band south of the Sahara from Mali to Uganda (White 1983; map: very approximate, from White 1983). This forest is biogeographically closest to Miombo woodlands among other African vegetation types (Linder et al. 2012).
Even LTRF in Africa can have a substantial component of ECM Fabaceae. Thus Gilbertiodendron dominates considerable areas of the Congo Ituri rainforest, Microberlinia dominates Guineo-Congolian forests in Cameroon, and other Detarieae dominate parts of the coastal forest from Sierra Leone to western Gabon, and again in the periphery of the Zaire basin (White 1983). Indeed, a caesalpinioid Biafran forest subtype has been recognised, and here, of 34 genera recorded, 28 are members of Detarieae, and 11 of these are described as being characteristically gregarious (Letouzey 1968). Newbery (1997) noted that Detarieae in Cameroon LTRF grew on poor soils and seemed to be able to control the flow of phosphorus through the ecosystem to their own benefit, however, fertilization with phosphorus had little effect on their growth (Newbery et al. 2002); Van der Burgt & Eyakwe (2008) give information about a ca 35 km2 caesalpinioid-dominated area in the Korup Forest. Gilbertiodendron dewevrei, whose foliage, seeds, and perhaps even mycorrhizae are major food sources for elephants, etc. (Blake & Fay 1997), dominates ca 10,000 ha in the eastern Congo. There it has above-ground biomass of 394-411.1 Mg ha-1, about 74% of the total (Makana et al. 2011); it may occupy 88% of the total basal area in the forests it dominates (Hart et al. 1989). Bâ et al. (2011a) summarized information on dominance of Detarieae.
In the New World, the ECM Aldina (Faboideae) and the coppicing Dicymbe (both Detarieae) dominate forests in the Pakaraima Mountains in the central Guiana Shield region (McGuire 2007b; M. E. Smith et al. 2011). The latter in particular supports a rich community of fungi (Henkel et al. 2012) and has a remarkably high basal area of 38.4-52.5 m2 per hectare, around 25(-40) m2 being more normal figures (Henkel 2003). Peltogyne (Detarieae: ?mycorrhizae) is one of the rare monodominants of the Amazon, where it occupies ca 53% of the basal area of trees 10 cm or more in d.b.h. on Maraca Island, Roraima, a figure that increases in proportion in larger trees (Nascimento et al. 1997). The Guianan upland ECM Eperua falcata, along with E. leucantha (mycorrhizae?), also Detarieae, are 50% more abundant (usually far more) than any other non-palm of the 20 most abundant hyperdominant trees (10 cm d.b.h. or more) of the Amazonian rainforest (Peh et al. 2011; ter Steege et al. 2013).
Not all monodominant legumes are ECM (Torti & Coley 1999; Torti et al. 2001; Peh et al. 2011). Legumes like the VAM Mora, a caesalpinioid legume not immediately related to Detarieae, dominates ca 37,000 hectares in Trinidad (Beard 1946; Hart et al. 1989); two other species of VAM Mora may also be monodominants, as is the VAM (and clonal) Pentaclethra (Henkel 2003; Peh et al. 2011). The Old World Cynometra (Detarieae) also appears to be VAM (e.g. Connell & Lowman 1989; Peh et al. 2011), and Cynometra alexandri dominates ca 11,000 ha in Uganda (Eggeling 1947) and comes close to dominating (ca 31.5% of above-ground biomass) in some forests in the eastern Congo, indeed, four caesalpinioids there make up over 50% of the biomass (Makan et al. 2011). Cynometra forests do not accumulate large amounts of litter, but that is also true of the ECM Julbernardia (Torti et al. 2001).
Although the relationship between mono- or oligodominance of legumes in tropical forests in particular and the nature of their fungal associations is not simple, the combination of phylogeny, monodominance and mycorrhizal type in legumes is strong. Of the nine dominant tropical species listed by Hart et al. (1989), five are caesalpinioids, of which three are ectomycorrhizal Detarieae, and two are ectomycorrhizal dipterocarps, while all the dominants listed by Connell and Lowman (1989) were legumes. 12/22 of the tropical classical monodominants listed by Peh et al. (2011) are legumes, of which 4/9 whose mycorrhizal status is known are ECM plants (the others are Cynometra, Pentaclethra and three species of Mora). Of the other ecological attributes of these legumes (where known), all had poor dispesal, masting occured in all but two (two of the three species of Mora), and the seeds were medium-sized to large, being 5-117 g in weight (Peh et al. 2011). All told, these dominant tropical legumes are characterized by a syndrome of features that includes growing on poor soils, having large seeds with poor dispersal, accumulating litter, tolerating shade, etc. (e.g. Hart 1990; Torti et al. 2001; Alexander 2006; Bâ et al. 2011b). However, Newbery (2005, see Hogberg 1986) noted that mast fruiting had not been recorded from East African forest dominated by caesalpinioids. Interestingly, Gentry (1993) compared the ecological role of ECM dipterocarps in the Old World with that of caesalpinioid legumes in the New World, particularly on poor soils and under seasonal climates.
Other Fabaceae are conspicuous elements of various vegetation types world-wide (Lewis et al. 2005; Schrire et al. 2005). Thus Faboideae-Robinieae are an important component of the neotropical seasonally dry tropical forest (Pennington et al. 2009), while Inga (Mimosoideae), with some 350 species, is very conspicuous in neotropical lowland forests (Richardson et al. 2001b; Pennington et al. 2009). In the Cape fynbos vegetation there are some 250 species of Aspalanthus alone and in the West Australian kwongan over 135 species of Acacia (Cowling et al. 2000). There has been much diversification within a number of geographically-restricted clades of Indigofereae that grow in succulent biomes (Schrire et al. 2009).
Cluster roots have been reported in some Faboideae, including Lupinus, although they do not occur in all members of that genus; the overall appearance of such roots is rather regular and dauciform, but this carrot-like shape is made by the dense, spreading lateral roots, not by root hairs as in dauciform roots proper (Shane & Lambers 2005). Species of Lupinus with such roots (especially common in Old World), and some with ordinary roots (from the New World) release massive amounts of carboxylates (organic anions) such as citrate, sometimes in amounts up to 23% of dry mass, and these can replace organic or inorganic phosophorus on soil particles under alkaline conditions and so mobilize it (Lambers et al. 2013 and references). Since Lupinus can also fix nitrogen, it can be an aggressive pioneer on volcanic and other skeletal and nutrient-poor soils (Lambers et al. 2013).
Knoblauch et al. (2001) discuss the possible mode of action of the distinctive spindle-shaped non-dispersive protein bodies (= forisomes) that are common in the sieve tubes of Faboideae (e.g. Behnke 1981b; Behnke & Pop 1981; Peters et al. 2010; Müller et al. 2014). The forisomes can block the pores of the sieve plates when turgor pressure changes, and change shape and volume very quickly depending on the concentration of Ca2+ ions; ATP is not needed for this shape change (Peters et al. 2007, 2008, 2010). Within Faboideae, forisomes are absent from a number of Galegeae, many members of which - including those species of Astragalus studied - also lack calcium oxalate crystals (Peters et al. 2010).
Pollination Biology & Seed Dispersal.
Although one often thinks of the monosymmetric pea or papilionoid flower and its variants as characterising the family - bar the mimosoids - as a whole, this much underestimates the great variation in floral morphology in many "Caesalpinioideae" in particular. As Bruneau et al. (2005, p. 201) noted of caesalpinioid legumes, "zygomorphy is expressed as a multitude of homoplasious morphs". Detarieae in particular show much floral variation, with the complete loss of organs or whorls of organs being associated with major dislocations of developmental patterns (Tucker 2000; Bruneau et al. 2014). Within Faboideae (= Papilionoideae), papilionoid flowers are found only in a subset, albeit a large subset, of the clade and are probably derived within it. Thus the flowers of Swartzia, perhaps sister to all other Faboideae, are very different from those of all other Fabaceae in their single banner petal, numerous free, mostly infertile and very dimorphic stamens, and absence of nectar (Tucker 2003b), and there is considerable floral variation - but rarely papilionoid flowers - in other basal Faboideae (e.g. Mansano et al. 2002, 2004). Even if papilionoid flowers are not as widespread as one might think, flowers with banner petals are common in non-mimosoid Fabaceae. Heteranthy is notably common in Fabaceae, excluding Mimosoideae (Vallejo-Marín et al. 2010).
Hardly surprisingly, Fabaceae attract a diversity of pollinators that visit the flowers for various rewards; Lewis et al. (2000) summarize what is known about pollination in Fabaceae, especially in "Caesalpinioideae". Bat pollination is quite common in tropical members of the family (Fleming et al. 2009), bats visiting flowers with a variety of morphologies. Bee pollination is particularly common, Xylocopa bees alone visiting some 52 genera (Leppik 1966; Hurd 1978; Kalin Arroyo 1981; Lewis et al. 2000). Pollination in "Caesalpinioideae" is predominantly by polylectic bees, while oligolectic bees are commoner pollinators of Mimosoideae and some Faboideae. Oligolectic bees are more speciose in (warm) temperate regions, especially Mediterranean climates (Michener 1979; Kuhlmann & Eardley 2012), and that is where the latter two subfamilies are particularly common. North temperate megachilid osmiine bees like Hoplitis species of the Annonosmia-Hoplitis group collect pollen from concealed-pollen flowers of the family and/or members of Boraginaceae; polylecty is derived in this group of bees (Sedivy et al. 2013). The bees may visit these plants with very different floral morphologies because both have pyrrolizidine alkaloids and/or particular nutrients that are essential for the growth of the bee larvae (Sedivy et al. 2013). Faboideae are pollinated mostly by polylectic bees, and in a variety of ways, and the plants are a major source of both nectar and pollen (Goulson 2010: in the U.K.), pollen morphology is relatively uniform (ref.?). Interestingly, within the tropics bees seem to be commonest in the New World (Michener 1979), and woody Fabaceae are especially diverse there.
The monosymmetric papilionoid flower has a more or less erect banner petal, two wing petals, and paired interlocking keel petals enclosing the stamens; bee pollination is the norm here (for pollination in keel flowers in general, see Westerkamp 1996, 1997). The micromorphology of the epidermis differs between different petals of a single flower. The outer surfaces of the wing petals in particular are variously sculpted (Tewari & Nair 1979), with pockets and folds that afford footholds for the pollinator (Le Roux & van Wyk 2012) in Faboideae, at least (Stirton 1981; Ojeda et al. 2009). Colour patterning of the corolla is conspicuous, as in Lupinus, Caesalpinia, and Bauhinia, and is always on the adaxial banner petal; these petals may also absorb ultraviolet light. The colour patterning on the standard of Hardenbergia violacea (Faboideae) may even mimic an anther (Lunau 2006). Although the flowers of Cercis are only superficially similar to those of Faboideae (Tucker 2002a), they, too, have keels and are similar functionally, although Cercis lacks the sculpturing on the wing petals that is common in Faboideae. In some Caesalpinia s.l. the abaxial sepal is coloured and more or less functions as a keel.
The nature of the reward for the bee varies, as is how the pollen is presented and where any nectar is to be found. When the androecium is monadelphous, i.e. the filaments of all the stamens are connate, there is no nectar and the reward for the pollinator is often pollen. This can be delivered by a pump-type secondary pollen presentation mechanism: The bee lands on the keel, and the style then forces pollen out of the tip of the keel in a tooth paste-like strand, as in Lupinus. If the androecium is diadelphous - nine stamens are connate and a single adaxial stamen is free - the reward is often nectar, the nectary lying between the filament tube and gynoecium and being quite variable in morphology; Indigofera even has short, nectar-secreting spurs (see also Vogel 1997; Davis et al. 1988). Other taxa like Cytisus, Desmodieae and Indigofera have explosive pollination. Here the style, held under tension, is released when the pollinator lands, as it were breaking the keel and scattering pollen over the insect (e.g. Polhill 1976); such flowers can be visited only once. Secondary pollen presentation also occurs in Vicieae and a number of other Faboideae. Here the pollinator picks up the pollen from the pollen brush at the end of the style; this has evolved perhaps eight times (e.g. Lavin & Delgado-S. 1990). In the asymmetrical flowers characteristic of Phaseolinae the labellum is twisted, forming a tube rather like an elephant trunk; this is why Vigna caracalla is called the corkscrew vine (c.f. Pedicularis: Orobanchaceae). When the bee lands on the flower, pollen is extruded from the end of the tube (Delgado-Salinas et al. 2011). Endress (2012) suggested that floral asymmetry was a key innovation in Phaseoleae.
Buzz pollination is quite common in Fabaceae. It occurs throughout Cassia, Chamaechrista and Senna ("Caesalpinioideae": Lewis et al. 2000). Here the anthers have four different modes of development (Tucker 1996b). The flowers of Senna are often enantiostylous and lack bracteoles (enantiostyly is likely to have been acquired once, although also subsequently lost); the anthers are basifixed and porose. There are three (or more) stamen morphs: three abaxial staminodes, four middle medium-sized stamens from which pollen is taken by the bees, and three longer abaxial stamens pollen from which is actually involved in pollination (see Tucker 1996b; Marazzi & Endress 2008; Marazzi et al. 2007). Cassia s. str., with dorsifixed anthers, also has three stamen morphs. The filaments are curved and the anthers have slits or basal pores. Finally, the largely herbaceous Chamaecrista is also enantiostylous; the stamens have two morphs in different whorls, the filaments are short, and the basifixed anthers dehisce by pores and have a velcro-like line of hairs (Tucker 1996b). There is considerable variation in stigma morphology; the stigmas are porose to crateriform and may have an exudate (Dulberger et al. 1994; Marazzi et al. 2007; Costa et al. 2014). Details of pollination are poorly known, in particular, how the pollen gets to the receptive surface in stigmas with very small pores, but Westerkamp (2004) suggests that in some species of both Senna and Chamaecrista the orientation of the anthers is such that the pollen ejected when the flower is vibrated misses the bee entirely, but it bounces off the petals and then lands on the bee's back - whence it is removed by the stigma; enantiostyly is an integral part of this remarkable pollination mechanism.
Bird pollination is scattered in the family. The some 105 species of Erythrina are pollinated by perching (sun) and hovering (humming) birds, and both floral morphology and how the flowers and inflorescences are held varies according the requirements of these different visitors (Bruneau 1997).
Mimosoideae have very different flowers from those of other Fabaceae. Numerous small, polysymmetric flowers are grouped into attractive units, all flowers opening at about the same time. The pollen grains are frequently aggregated into polyads which are caught in a cup-shaped stigma that is of the appropriate size for the polyad of that species, and there are also about as many ovules in the ovary as there are pollen grains in the polyad (Banks et al. 2010; Kenrick 2003: implications of this pollination mechanism for the breeding system). Banks et al. (2011) note that all the pollen grains of a polyad form a single harmomegathic unit. In Calliandra s. str. the polyads sometimes have an associated sticky mucilage body by which they are attached to the pollinator, but the stigma is much larger and capitate and the polyads adhere to its surface (Prenner & Teppner 2005; Greissl 2006, c.f. in part Teppner 2007). Bats may also be pollinators, as in Parkia (Bumrungsri et al. 2008 and refs.). For more information on locellate anthers (scattered in the clade), polyads, anther dehiscence, etc., in Mimosoideae, see Prenner and Teppner (2005), Teppner (2007) and Teppner and Stabentheiner (2007, 2010) and references.
The legume s. str. is a single carpellate fruit that dehisces explosively, the two valves of the carpel twisting as they separate. Such fruits have two layers of lignified fibres, at least one of which is oblique to the long axis of the fruit (Fahn & Zohary 1955). A legume so defined is common in European-North American Faboideae, but also in Bauhinia, Duparquetia, Detarieae (where seeds of emergent Tetraberlinia moreliana may be thrown some 60 m - e.g. van der Burgt 1997), and so on. The fruits of Cercis are not explosively dehiscent, but are otherwise similar; they are also typologically rather similar to the fruits of Myristica, the nutmeg! Overall there is a great diversity of fruit morphology in the family, including variously winged fruits, fleshy fruits, fruits breaking up into single-seeded units in different ways, and fruits modified for external animal transport with spines and hooks, for example, the velcro-like hooks on Desmodium (hence its common name, beggar's ticks) and the indehiscent, spiny, spirally-coiled fruits of many species of Medicago (for their evolution, see Fourquin et al. 2013). In Trifolium the calyx and corolla are both involved in fruit dispersal. Arillate seeds are common and are eaten by birds in particular. Seeds of Abrus precatorius, Erythrina and Pithecellobium have red and black color patterns on the coat and mimic the color contrasts of these arillate seeds (Foster & Delay 1998; c.f. transference of function, Corner 1958), but chewing the seeds of Abrus precatorius is not recommended. In many taxa, especially those with explosively dehiscent fruits, the seed coat is very hard and may need scarification for germination to occur (for fruits and seeds, see Corner 1951; van der Pijl 1956; Kirkbride et al. 2003; etc.). Close to a thousand Faboideae are myrmecochorous, and myrmecochory occurs in many species of Acacia s. str. and other Australian Fabaceae (Mckey 1989; Orians & Milewski 2007; Lengyel et al. 2009, 2010); independent evolution of this dispersal mode has occurred several times within the family. For other aspects of the ecology of seed coats, see Souza and Marcos-Filho (2001).
Plant-Animal Interactions. Herbivory by foliovorous insects is often quite marked, herbivores in general preferring to fed on nitrogen-enriched plants (Simonsen & Stinchcombe 2014 and references). Cassia fistula is sometimes almost defoliated by caterpillars of pierid butterflies, while up to one third or more of the developing foliage of species of Inga may be eaten by herbivores (Kursar et al. 2009). There may be interesting interactions between the nature of rhizobial infections and the effects of herbivory. Medicago, for example, can have roots with nodules formed by N-fizing or non-N-fixing ("exploitative") rhizobia, and plants with mixture of exploitative and non-exploitative rhizobia did less well than plants with only N-fixing rhizobia under conditions of no herbivory, but the two performed equally poorly if there was herbivory (Simonsen & Stinchcombe 2014).
Associations of insects and Fabaceae are often quite close. Caterpillars of Lycaenidae-Riodininae-Riodinini, Lycaenidae-Curetinae and especially Lycaenidae-Lycaeninae-Lycaenini butterflies are often found on Fabaceae (Ehrlich & Raven 1964; Fiedler 1991, 1995), as are larvae of the some 260 species in 15+ genera of Coliadinae and Dismorphiinae (Pieridae) butterflies (Braby & Trueman 2006: a quarter of the records, see also Brassicales and Santalales), indeed, species of Fabaceae may be the original food plants of Pieridae (Braby & Trueman 2006; Wheat et al. 2007; Fordyce 2010). The diversity of caterpillars, especially that of "basal" butterfly groups, including Baronia, sister to all Papilionidae (Heikkilä et al. 2011), on Fabaceae is such that Janz and Nylin (1998) and Braby and Trueman (2006) suggested that Fabaceae might be the springboard for host-plant diversification of butterflies feeding on angiosperms in general (see also the introduction to Fabales), although that then would mean that diversification of these butterflies would be Tertiary, given the suggestions for the age of Fabaceae (see also above).
Some 70% of the 1,700 seed beetles, bruchids (Chrysomelidae-Bruchinae [used to be Bruchidae]), are associated with Fabaceae, the legume-feeding seed beetles perhaps beginning to diverge around 60 m.y.a., around about the time of origin of Fabaceae themselves (Kergoat et al. 2011). Stem Bruchinae are rather older, and they may initially have eaten members of Arecaceae (q.v.); from Faboideae, they moved on to other groups following the chemistry of the plants (esp. Kergoat et al. 2005a, b; also Johnson 1989, 1990: Acanthoscelides; Birch et al. 1989: chemistry of the interaction; Janzen 1969: the complexity of the association; Kato et al. 2010: importance of female oviposition preferences). The larvae are specialized seed-eaters, and particular groups of bruchids may be associated with particular groups of Fabaceae (e.g. Kergoat et al. 2011 and references). Two clades, made up largely of New World Acanthoscelides and predominantly Old World Bruchidius, dominate, and their radiation may have been contemporaneous with that of their hosts, largely Mimosoideae and Faboideae (and later some Malvaceae, in particular); they can detoxify the non-protein amino acid, L-canavanine (Kergoat et al. 2005b). For estimates of when particular groups of bruchids diversified on particular clades of Faboideae, see Kergoat et al. (2011). The pattern of association of bruchid groups with mimosoids is interesting; individual bruchid genera tend to be found on adajcent pectinations of the mimosoid phylogenetic tree (Kergoat et al. 2007).
For the diversification of Psyllidae (jumping plant lice; Hemiptera-Sternorrhyncha) on Macaronesian Faboideae-Genisteae, see Percy et al. (2004). Psyllids are quite common there, and the diversification of psyllids has been dated to around 3 m.y.a., well after that of their hosts which occurred ca 8 m.y.a. (Percy et al. 2004).
Pinzón-Navarro et al. (2010) discuss the weevils found on Inga; up to 43 species of this speciose genus may coexist at a single site, and this may in part be possible because species differ considerably in antiherbivore defences, the defences varying independently between the species (Kursar et al. 2009).
In another variant of insect-plant relationships, the flowers of Crotalaria are visted by Danainae and Ctenuchidae because the pyrrolizidine alkaloids they contain are used as the basis of the pheromones of these lepidoptera (also Asteraceae, and wilting plants of some Boraginaceae: Edgar et al. 1974; Pliske 1975; Boppreé 1986). Crotalaria is also involved with arctiid moths such as Utetheisa, its secondary metabolites providing defence for the young, etc. (Eisner & Meinwald 1995).
Rather generalized legume/ant associations are very common in Fabaceae and are mediated by extrafloral nectaries. The nectar secreted, which usually contains sucrose, attracts ants that can protect the plant against herbivorous insects. Such nectaries have possibly evolved some 35 times in the family, and have also subsequently been lost and even regained (e.g. Marazzi et al. 2011, 2015; see also McKey 1989). They are notably common in Mimosoideae (but only one origin) and are found towards the base of the petiole, on the rachis, and sometimes on petiolules. They are less common in caesalpinioids, although they may be represented by tufts of hairs (Pascal et al. 2000), and still less common in Faboideae, although with many origins there (Marazzi et al. 2015).
The presence of such extrafloral nectaries characterises a major clade within Senna. There they may be a "key innovation" that is involved in the diversification of that clade, which is both much more speciose than its sister clade (68 species, no nectaries, versus 282 species with nectaries) and has speciated significantly faster. The extrafloral nectary-bearing clade may have exploited the new habitats that became available in South America after the Andean uplift (Marazzi et al. 2006; Marazzi & Sanderson 2008, esp. 2010). Marazzi and Sanderson (2010) suggest a crown-group age for this clade of some 40.8-30.6 m.y., that is, somewhat before the Andean uplift (ca 30 m.y.a.). But Marazzi and Sanderson (2010) also noted that Simon (2008) had found that the loss of extra-floral nectaries characterized a large clade of Mimosa that was far more speciose than its sister clade; the ratio of species in the sister taxa with and without extrafloral nectaries there is 15:515 (Simon et al. 2011). Furthermore, a less conspicuous and organized kind of extrafloral nectary characterizes a separate clade of Senna (Marazzi et al. 2013b).
More intimate ant-legume associations also occur. The close association of Pseudomyrmex ants with some members of the old Acacia subgenus Acacia (= Vachellia), including the swollen-thorn acacias such as V. sphaerocephala, are well known. The plant provides protein-rich Beltian bodies at the ends of each leaflet (the leaves have many leaflets, even for Acacia s.l.) as food for the ants, and swollen stipular thorns serve as their homes (Janzen 1967b, 1974b; Webber & McKey 2009). The ants also take nectar from extrafloral nectaries; interestingly, unlike the nectar normally produced by these glands, the nectar is sucrose-free, the ants lacking the invertase needed to break down sucrose (Kautz et al. 2009). Perversely, species of Acacia with low nectar rewards are derived from those with higher rewards; species that offer only low rewards are often colonized by exploiter ants that do not defend the plant (Heil et al. 2009). Complex interactions between protease inhibitors in the plant and proteases in insects may help deter other than the mutualist ants from eating the Beltian bodies (Orono-Tamayo et al. 2013).
There are other examples of close ant-plant relationships in Fabaceae (McKey 1989 for a list). In the common African Leonardoxa africana (Detarieae) a third party, an ascomycete, is central to the relationship. Nitrogen from the ants first initially moved more into the fungus than the plant (Defossez et al. 2010), ant larvae ate the fungi (Blatrix et al. 2012: see also similar associations in Tachigali), although over time the nitrogen became distributed about equally among all three partners (Defossez et al. 2010). For plant-ant signalling in this association, see Vittecoq et al. (2011); Brouat et al. (2001) thought that the size and shape of the prostoma, the more or less unlignified area of the stem through which the ant entered the plant, could in some cases be linked with comparable attributes of the head of the ant involved in the association.
The toxic indolizidine alkaloid, swainsonine, is found in Astragalus (species with it are called "locoweeds"), Oxytropis and Swainsona itself, and it causes a serious, sometimes fatal, disease in cattle (for its synthesis by associated fungi, see Pryor et al. 2009; Ralphs et al. 2008). The non-protein amino acids found in many Fabaceae (see below) may also be toxic, while the Australian Gastrolobium (Mirbelieae) produces the toxic sodium monofluoroacetate (Chandler et al. 2001).
Indeed, the diversity of secondary metabolites in Fabaceae, perhaps especially in Faboideae, is remarkable. For instance, about 28% of all known flavonoids and about 95% of the isoflavonoid aglycone structures - over 1,000 alone - have been found there, and isoflavonoids are restricted to Faboideae. Isoflavonoids are both phytoalexins involved in plant defence and may also play a role in nodulation (Hegnauer & Grayer-Barkmeijer 1993; Reynaud et al. 2004). Flavonoids lacking the 5-hydroxy group are characteristic of Fabaceae (Seigler 2003), but I do not know at what level they are apomorphic. In general Fabaceae have a very distinctive nitrogen metabolism. Non-protein amino acids are common (see e.g. Fowden et al. 1979), and nitrogen in the xylem sap is transported as a mixture of amino acids, amides, and sometimes also ureides; very little is transported as nitrate. Wojciechowski et al. (2003, 2004, see also Wojciechowski 2003) note that the distribution of some non-protein amino acids are systematically interesting. Thus canavanine production seems to have originated in the ancestor of a major group of Faboideae that includes mirbelioids, millettioids, robinioids, and the IRLC, and has been dated to 54.3 ± 0.6 m.y.a. (Lavin et al. 2005 - see tree above). L-canavanine, which can be taken up in place of the normal amino acid L-arginine, may have potent effects on herbivores, although some can detoxify it (e.g. Rosenthal 1990, 2001 and references; Kergoat et al. 2005b; Huang et al. 2011: non-protein amino acids in general). L-canaline is rather like the amino acid ornithine; both L-canaline and L-canavanine serve as nitrogen reserves for the plant. Pea albumin, a small sulphur-rich peptide with insecticidal properties, is known only from Faboideae where it may be a synapomorphy for the [hologalegina + millettioid] clade (Louis et al. 2007: it is lost in some/all robinioids). Interestingly, canavanine and alkaloid production are mutually exclusive in legumes, while within the genistoids quinolizidine and pyrrolizidine alkaloids are similarly mutually exclusive (Wink 2008).
There are also more conventional chemical deterrents in Fabaceae, and a number of species have cyanogenic glucosides. Here plant-insect interactions have been studied in detail, for instance, those between the cyanogenic host (Lotus corniculatus) and caterpillars of the burnett moth Zygaena filipendulae; the latter can also synthesize the cyanogenic compounds itself (Zagrobelny & Møller 2011: references to other systems). Alkaloid glucosides are known, e.g. from Vicia, and Pentzold et al. (2014) discuss ways insects have of getting around such defences. Astragalus can accumulate the toxic sulphur-antagonist, selenium (El Mehdawi et al. 2012).
Bacteria and N-Fixation.
Many Fabaceae have a close association with nitrogen-fixing bacteria which grow inside irregular, pinkish-coloured nodules on the roots (Sprent 2009 for a summary), the α-proteobacterium Rhizobium is the best-known genus involved. Nodulation is especially widespread in Faboideae and Mimosoideae, but it is less common in "Caesalpinioideae", although occurring e.g. in Chamaecrista. In general, nodulation is very common indeed outside the tropics, less common in the tropics (Sprent et al. 2013). Although most Faboideae are nodulators (Sprent 2000, 2001, 2007) and the nodulating Swartzia (derived nodule morphology) and immediate relatives may form a clade sister to the rest, or most of the rest, of the subfamily (see below: Ireland et al. 2000; Pennington et al. 2000; Lavin et al. 2005), other Faboideae that are in clades basal to that including the bulk of the subfamily do not nodulate. Root nodule morphology may help delimit groups of genera in Faboideae (Wojciechowski 2003), but nodule morphology is independent of the particular bacterium involved, being controlled by the plant (Angus et al. 2013; Agapakis et al. 2014).
Some aquatic legumes in both Mimosoideae (Neptunia) and Faboideae (Aeschynomene) form stem nodules, albeit sometimes also associated with adventitious roots. In Aeschynomene the ability to form such nodules has evolved more than once, and members of a clade of this genus can form nodules with Bradyrhizobium even though they have lost Nod-genes (the bacteria enter via cracks in the stem), furthermore, several strains of Bradyrhizobium are involved and some are photosynthetic (Chaintreuil et al. 2013).
Nodule formation is initiated by the exudation of flavonoids, isoflavonoids, and other attractants by the host and infection of a root hair by a bacterium. There are other ways in which the plant becomes infected, including through cracks in the epidermis, perhaps the plesiomorphic condition, as in Faboideae-Dalbergieae and -Genisteae (Cannon et al. 2010; Vessey et al. 2004; Okubo et al. 2012; Chaintreuil et al. 2013); nodulation near lateral roots also occurs (Sprent et al. 2013 for a summary). The nodules are anatomically rather like stems in having peripheral vascular bundles, the bacteria being in the pith (Franche et al. 1998), however, nodule origination occurs where lateral roots develop, at least in Faboideae (op den Camp et al. 2011, see also below).
Nodule formation involves the production of Nod factors by the bacterium, although in a few nodule-forming α-proteobacteria (see below) such as the photosynthetic Bradyrhizobium canonical nodABC genes are absent (Giraud et al. 2007). Nod factors are lipochito-oligosaccharides (LCOs), made up of a chain of 3-5 N-acetyl-D-glucosamine units, variously substituted and with a 16-20 C fatty acid attached. The plesiomorphic infection morphology is that of persistent infection threads and long-lived nodules (see also Parasponia [Cannabaceae]), more derived is the absence of infection threads, the mitosis of infected cells, and a short life span of the nodule (de Faria & Sprent 1995; Corby 1988: survey of nodule morphology; Sprent 2005: nodule distribution, see also J. J. Doyle 1994, 1998; J. J. Doyle et al. 1997; Lavin et al. 2001; Oono et al. 2010). Infection threads are invaginations of the wall of the root hair through which bacteria reach the apoplastic area beneath the epidermis, and by the development of further threads they move more deeply into the root. They eventually move into the cell by endocytosis; one or a few bacteria (now known as bacteroids) are enclosed by a plant membrane, the whole forming an organelle-like symbiosome (Rae et al. 1992; Streng et al. 2011, summary). Symbiosomes, organelles bounded by a host-derived membrane, contain one or more bacteria (Sprent et al. 2013). Persistent infection threads and nodules of indeterminate growth are found in "Caesalpinioideae" and also in some Faboideae like Pisum and Vicia (Naisbitt & Sprent 1992; Rae et al. 1992). In such nodules symbiosomes are formed in cells that are no longer meristematic, the meristem continuing to produce a supply of cells that are serially infected by the persistent infection threads. In determinate nodules, such as occur in Phaseolus, symbiosomes form in cells of the nodule meristem, and transmission is by cell division (Rae et al. 1992). Bacteroid differentiation is either reversible, little morphological change having occurred, or non-reversible; in the latter case, which is much less common (Oono et al. 2010), bacteroids become swollen, and N-fixing by these swollen bacteroids is more efficient than by non-swollen bacteroids (Oono & Denison 2010).
In Faboideae, there seems to have been cooption of genes originally involved in lateral root origination after a genome duplication event ca 54 m.y.a. (op den Camp et al. 2011; Q.-G. Li et al. 2013); this happened after the divergence of Faboideae from N-fixing clades such as Chamaecrista, which do not have this duplication (Cannon et al. 2010) and so probably have a different mode of nodule formation. See also Hirsch and LaRue (1997), Couzigou et al. (2012) and Chaintreuil et al. (2013) for the complex origin of the nodule developmental pathway.
Details of the evolution of nodulation in Fabaceae are still not well understood. The ability to nodulate has probably been acquired several times within the family. Genes involved in the association tend to be clustered in symbiotic plasmids or on symbiosis islands within the genome and move about relatively easily by lateral gene transfer (Agapakis et al. 2014), and several nod genes aggregate to form the nodABCIJ operon that is common in α-rhizobia (Aoki et al. 2013, see also below); this enables bacteria to become endosymbionts in a single step (Maclean et al. 2007). Indeed, in Ethiopia it was found that there is both vertical transmission of these gene complexes as well as horizontal transmission of infection islands from introduced strains of nodulating bacteria to native strains (Aserse et al. 2012). In eastern North America legume hosts select for particular Bradyrhizobium strains, and independent of this particular variants of the infection island are exchanged between the different bacteria (Parker 2012). Strains of Bradyrhizobium may be metabolically quite different, conversely, quite different legume bacterial symbionts may share more genes than Rhizobium leguminosarum, for example, shares with the closely related but non-symbiotic Agrobacterium (Maclean et al. 2007). Symbiont specificity tends to be greatest in the IRLC clade (Faboideae), although genera like Astragalus are exceptions (Howard & Wojciechowski 2006). See also Ormeño-Orillo et al. (2013) for lateral transfer of nodulation genes. Further complicating the issue, rhizobia do not form resting spores, and it is not known how they persist in the soil - perhaps in biofilms (Hirsch 2010)?
As mentioned above, many nodulating bacteria are members of the proteobacteria α-2 subclass, but they do not form a monophyletic group, and several "species" are involved; Agrobacterium (crown gall tumour) and others are also members of this group (J. J. Doyle 1998; Sprent 2001). Bradyrhizobium associated with Fabaceae both in Australia and Ethiopia is very diverse, many species lacking names (Stepkowski et al. 2012; Aserse et al. 2012), and there is substantial temperate/tropical differentiation in the bacteria (Stepkowski et al. 2012).
Other important N-fixing bacteria associated with Fabaceae include Burkholderia and relatives, which are ß-proteobacteria not at all close to Rhizobium. These are quite common in the tropics, and can tolerate alkaline conditions (Sprent 2007; Angus et al. 2013). Not all fix nitrogen, for instance, some are human pathogens, but those that are effective nitrogen-fixing symbionts form two groups, one involved in symbioses with New World Mimosa and Mimosoideae and with the nod and nif genes on plasmids, the other, B. tuberum, nodulating African Faboideae-Crotalarieae and -Phaseoleae and with the nod and nif genes on the chromosomes (Bontemps et al. 2010; Agapakis et al. 2014). Other ß-proteobacteria form nodules, albeit ineffective, with Mimosoideae (Moulin et al. 2001; Sprent 2002; Elliott et al. 2007 and references), and some are even pathogenic, but these rarely nodulate. Surprisingly, a Burkholderia growing on Solanum was able to form nodules and fix nitrogen when on Phaseolus vulgaris (Martínez-Aguilar et al. 2013). It is often suggested that genes involved in nodulation moved from α- to ß-proteobacteria, but it appears that nodIJ genes, at least, may have evolved following a gene duplication in ß-proteobacteria and then moved and became part of the nodABCIJ operon (Aoki et al. 2013).
For a mutation that improves nuclear calcium signalling at an early stage in the development of symbioses, see Venkatheshwaran et al (2012) - IRLC clade only (Lotus, Medicago)?
There are important fungus-legume interactions. Thus Mimosoideae (phyllodinous Acacia, Senegalia), Faboideae such as Aldina, perhaps Gleditsia, a group of five genera around Mirbelia, and in particular "Caesalpinioideae"-Detarieae, are ECM plants, but only very rarely also endomycorrhizal (ENM: e.g. Sprent & James 2007; S. E. Smith & Read 2008; Bâ et al. 2011a, b; M. E. Smith et al. 2011: see above). In the ECM associations of three species (two Dicymbe [Detarieae], Aldina) dominating in New World forests there were over one hundred species of mostly basidiomycete fungi involved (M. E. Smith et al. 2011). Although not that many species are known to be ECM, their ecological impact is disproportionately great for their numbers; for further details, see Ecology & Physiology above and clade asymmetries. Endomycorrhizal fungi occur in root nodules in several species (but not in Lupinus, see also above), although their importance there is unclear (Scheublin & van der Heijden 2006).
In Oxytropis kansuensis the toxic indolizidine alkaloid, swainsonine, is synthesised by the endophyte Undifilum, an imperfect stage of Pleosporaceae, an ascomycete (Pryor et al. 2009; see also Reyna et al. 2012). Swainsonine is also found in Astragalus and Swainsona itself; the related fungus Embellisia is also implicated in this association (Ralphs et al. 2008).
Rusts show interesting patterns of distribution on Fabaceae. Uromyces is found predominantly on herbaceous Faboideae, but also on Bauhinia and one or two other non-Faboideae), while Ravenelia is found on woody members of the family, "Caesalpinioideae" (but not Bauhinia) and especially Mimosoideae (Savile 1976, 1979a, b; El-Gazzar 1979). In some species of Ravenelia the teliospores, thick-walled spores in which nuclear fusion and then meiosis occur, are aggregated into groups, and these telial heads may mimic the groups of pollen grains (polyads) that are common in Mimosoideae. Stingless Trigona bees pick up both telial heads and polyads as they forage for pollen, so helping disperse the fungus. Interestingly, Ravenelia is only very rarely found on Acacia, and the distributions of rusts, acacias and trigonid bees all break at about Wallace's Line; thus Ravenelia is not native to Australia, Acacia s. str. is centred on Australia, etc. (El-Gazzar 1979; Savile 1979b).
Bacteria and Fungi together.
Fabaceae include most ECM plants that also fix nitrogen, a rather uncommon combination (for Alnus [Betulaceae], see Walker et al. 2013), although relatively little is known about their eco-physiology. Emdomycorrhizal Fabaceae are commonly associated with N-fixing bacteria (Bâ et al. 2011b). In Acacia mangium nodulation and leaf nitrogen are increased if the plants are ECM (Diagne et al. 2013), while in endomycorrhizal Fabaceae phosphorus uptake by the fungus may affect N fixation (Walker et al. 2013 and references). Otherwise, details of interactions between plant, fungus and bacterium in such associations are unknown.
Vegetative Variation. Although most Fabaceae have once or twice compound leaves, leaflets with entire margins, and pulvini associated with leaves and leaflets, there is extensive variation on this theme. Thus palmate leaves occur in Lupinus, serrate margins in Cicer, Medicago, etc., and unifolioliate leaves are scattered throughout the family. A number of Faboideae (e.g. Vicia, Pisum) are tendrillar vines, the tendrils being modified terminal leaflets; in Lathyrus aphaca the photosynthetic function of the leaf is taken over by the large stipules, the rest of the leaf being a unbranched tendril, while L. nissolia lacks tendrils and has a phyllodinous leaf (see Kenicer et al. 2005 for a phylogeny). In some taxa compound leaves are reduced to a single more or less connate pair of leaflets, as in Bauhinia, named after the botanical brothers Caspar and Jean Bauhin, and Cercis (Owens 2000).
In general, angiosperm leaf development is associated with the activity of the KNOX1 gene, and this is true of plants with compound leaves incuding many Fabaceae. However, in the IRLC clade (Faboideae) the KNOX1 gene is not - or rather differently - expressed in the developing leaves, while FLO/LFY genes, normally floral meristem identity genes, are expressed both in the leaves and in the flowers (Hofer et al. 1997; Wang et al. 2008; Peng et al. 2011; Townsley & Sinha 2012). The leaves of the IRLC clade lack pulvini, which are present in other Fabaceae (Champagne et al. 2007; Rosin & Kraemer 2009).
In Acacia s. str. (the old subgenus Phyllodinae), the leaves of the mature plant are much modified undivided structures flattened at right angles to the plane of flattening of a normal leaf; they are often called phyllodes; seedlings and regeneration shoots can also have normal-looking once or twice compound leaves. In the early development of normal leaves of Fabaceae two rows of adaxial meristems produce the leaflets/pinnae, and these become lateral in position by secondary reorientation. In the phyllodes of Acacia there is a single, broader adaxial meristem that develops into the entire leaf (Kaplan 1980); there is no reorientation, hence the plane of flattening of the phyllode. Complicating the issue, in species of Acacia like A. verticillate these phyllodes are densely set along the stem, some are associated with stipules and buds and have a nectary, but others are simply a flattened, needle-like process (Kaplan 1980); the relationship between the two kinds of phyllodes is unclear.
Some species of Mimosa and other genera have leaves that are sensitive to touch, stimulus transmission occurring as membrane depolarisation is propagated down the petiole and along the stem; folding of the leaf is caused by tugor changes in the cells of the pulvini at the bases of the leaf and leaflets (for the anatomy of the pulvinus, which has an endodermis, see Rodrigues & Machado 2007). Simon et al. (2011) suggest that sensitive leaves have evolved ca six times in Mimosa alone, although a full understanding of the evolution of this feature depends on more extensive studies on this and related phenomena in legume leaves. Thus in Albizzia (Samanea) saman, there are similar movements as the leaflets fold towards the evening when the light is failing, or just when there is heavy cloud cover, this behaviour being responsible (in some tellings of the tale) for the name of this plant, the rain tree. In Desmodium gyrans the single pair of lateral leaflets move intermittently without being touched, the speed of movement increasing with the temperature.
Economic Importance. Weeden (2007) discusses the diversity of genetic changes involved in domestication of legumes. For information on the domestication of soybean (Glycine max), common bean Phaseolus vulgaris, pea (Pisum sativum), the azuki bean (Vigna angularis) and relatives, see papers in Ann. Bot. 100(5). 2007, and for these taxa and lentil (Lens culinaris), see Fuller (2007). For the peanut, Arachis hypogea, see Krapovikas and Gregory (1994), for its domestication, see Dillehay et al. (2007) and for its phylogeny, see Friend et al. (2010), and for the domestication of the lima bean, Phaseolus lunatus, see Serrano-Serrano et al. (2010), and for much information on alfafa, Medicago sativa, see Small (2011).
Genes & Genomes. A whole genome duplication seems to have occurred prior to the divergence of Dalbergieae (Bertoli et al. 2009). There have been major changes in chromosomal organisation in Faboideae in particular that, apart from their intrinsic interest, provide a considerable amount of phylogenetic structure. The chloroplast genome is notably labile, both in terms of sequence (Kua et al. 2012) and structure (see Martin et al. 2014 for a summary). Most Faboideae have a 50kb inversion in the trnL intron in the large single-copy region of their chloroplast genome, however, taxa like Swartzieae, Cladrastis, and a few others, lack this inversion (J. J. Doyle et al. 1996, 1997; Pennington et al. 2001; Wojciechowski et al. 2004). The loss of the chloroplast inverted repeat characterises a largely temperate, epulvinate, herbaceous and very speciose group, the IRLC clade (see above: Wojciechowski 2003 and references); the woody Wisteria is also a member of this clade. The IRLC clade is characterized not only by the loss of the inverted repeat, but the leaves lack pulvini and differ in details of development (see above), there are CA primordia in the flower, A initiation is bidirectional, and there is overlap in the timing of C, A, and G initiation (Naghiloo & Dadpour 2010). All members of the IRLC clade lack the clpP intron, while the rps12 intron has been lost from all members of the clade examined except Wisteria, Callerya and Afgekia - but not Glycyrrhiza - c.f. the tree above (Jansen et al. 2008; Wojciechowski et al. 2008; see also Saski et al. 2007;; Cai et al. 2008). Indeed, genome evolution in taxa that lack the inverted repeat has been considerable (Magee et al. 2010). Desmodium and possibly related genera (MILL) have also lost the rps12 intron (it has moved to the nucleus) as well as the srp12 intron (Doyle et al. 1995; Bailey et al. 1997; Jansen et al. 2008). ORF84 has been lost many times, and accD (= ORF512, zpfA) has also been lost (Doyle et al. 1995). Both the rps16 and ycf4 genes are lost in most Faboideae (Doyle et al. 1995; Jansen et al. 2007). Bertoli et al. (2009) link genome regions that are variable with the presence of retrotransposons.
Transmission of plastids may be biparental (Corriveau & Coleman 1988). Cytisus purpureus forms a well-known graft hybrid with Laburnum anagyroides (+ Laburnocytisus adamii; see Herrmann 1951 for another example); the epidermis alone is Cytisus tissue, and any seeds, being derived from cells from deeper layers, will give Laburnum plants. However, the graft hybrid often breaks down, resulting in branches that are pure Laburnum anagyroides or pure Cytisus purpureus.
Chemistry, Morphology, etc. The occurrence of galactomannans, storage polysaccharides, in seeds of Fabaceae and the ratio of galactose to mannose in them may be of phylogenetic interest (Buckeridge et al. 1995, 2000a, b). Despite the diversity of secondary metabolites in the family, correlation of metabolites with clades is for the most part poor (Wink 2013). Characters of caesalpinioid woods include rays that are usually more than 20 cells tall, presence of silica bodies, and axial canals (Evans et al. 2006); I do not know how these fit on to the current tree. Some Mimosoideae and Faboideae have leaves that are rich in silica (Westbrook et al. 2009).
Mirror image flowers are scattered in non-mimosoid Fabaceae (Tucker 1996b). Details of hypanthial evolution within Fabaceae are unclear; it seems to have become much reduced and lost several times. The "normal" (for flowering plants) floral orientation of Mimosoideae with the median sepal adaxial and the median petal abaxial is secondary; in some 4-merous Mimosoideae the median petal is adaxial (Prenner 2011). Although the normal orientation is also found in caesalpinioids like Ceratonia, the inverted orientation occurs in Cercideae (see Tucker 1989; Herendeen et al. 2003; Luckow et al. 2005), Duparquetia, many other caesalpinioids, and Faboideae; the orientation of the single carpel is the same in all.
The numerous papers by Shirley Tucker are an essential starting point for any understanding of floral morphology and development in Fabaceae. The parts of the flowers of most Fabaceae develop in the unusual sequence sepals-carpels-petals-outer stamens-inner stamens, and there are other distinctive features of their development (e.g. Champagne et al. 2007; Feng et al. 2006; Wang et al. 2008). For variation in general patterns of floral development, see Prenner and Klitgaard (2008b); they emphasize the diversity of developmental patterns even within the corolla whorl, and that although both Duparquetia and Faboideae have the adaxial petal in the outermost position, yet the it has developmentally different pathways in the two. Prenner (2013b) surveyed floral development in Faboideae. Particularly when there is complete loss of individual floral structures in evolution, floral development can be greatly changed (Tucker 1988, 2000), however, as Bruneau et al. (2014) noted, in Detarieae organs in one whorl can be lost without much affecting the development of the rest of the flower.
For the adaxial sepal member in Mimosoideae, see Ramírez and Tucker (1990); they describe a variety of developmental pathways that result in the connate calyx of that subfamily. For more floral development in Mimosoideae, see Gemmeke (1982); stamens may develop centripetally on five main primordia. The cochlear-descending calyx aestivation, helically-initiated androecium, etc., of Calliandra s. str., are distinctive within Mimosoideae (Prenner 2004b). Prenner (2013b) found that petal initiation in Abrus, as in some other Faboideae, was simultaneous. For polyads, anther dehiscence, etc., in some Mimosoideae see Teppner (2007) and Teppner and Stabentheiner (2007) and references. Bauhinia has additional "staminodial" structures at the base of the ovary (Endress 2008c) that may have something to do with colleters.
For floral and inflorescence morphology, especially in Faboideae-Loteae, see Sokoloff et al. (2007a). Pennington et al. (2000) discussed floral evolution in "basal" Papilionoideae, some of which like Swartzia have flowers with very derived morphologies. Androecial initiation in Swartzia can be both centripetal and centrifugal (Tucker 2003b). The pattern of initiation of the sepals and stamens in Faboideae is variable, by no means always being unidirectional (e.g. Prenner 2004a; de Chiara Moço & de Araujo Mariath 2009). The flowers of some Amorpheae have a stemonozone rather than a hypanthium, i.e. the staminal tube is adnate to the petals (McMahon & Hufford 2002). Prenner (2004c) suggested that a slight asymmetry in the early development of the androecium (the adaxial median stamen is initiated slightly off the median axis) occurs in more "basal" Faboideae and also in some "Caesalpinioideae".
Pollen variation in Fabaceae is quite considerable outside Faboideae (Bente Klitgaard, pers. comm.), the pollen of Duparquetia being unique in angiosperms (Banks et al. 2006). Hesse (1986) noted that both Bauhinia and Cercis - and Caesalpinia and Delonix - had pollen-connecting threads made up of something other than sporopollenin. Many Mimosoideae have polyads, which vary in size and also whether or not they are calymmate, i.e. with a common covering of ectexine. The recently-described Afrocalliandra has a 7-celled polyad (de Souza et al. 2013, also literature for mimosoid pollen); I have no idea how this develops. The style is at least sometimes hollow, although the cavity arises in various ways, including by lysigeny (Lersten 2004). The carpels may have five traces and are quite often open during development in "Caesalpinioideae", but not, apparently, in Cercideae, Mimosoideae or Faboideae (Tucker & Kantz 2001). The embryo sac of some Faboideae (?elsewhere) more or less protrudes into the micropyle, as in Archevaletaia (Maheshwari 1950). There is a great deal of variation in the development of the embryo suspensor, even within Faboideae, especially in Vicia where endopolyploidy can reach 8,000C (Lersten 1983; also Tucker 1987; Yeung & Meinke 1993; Rodriguez-Pontes 2008; Endo 2012b). Both a true endothelium and an integumentary endothelium may be present in Faboideae (Rodrigues-Pontes 2008 for discussion and references). The two recurrent vascular bundles lateral to the hilum are absent in "basal" Faboideae (Lackey 2009). For the aborting plumule in seedlings of Lotus and Coronilla and their relatives, see Dormer (1945).
For additional general information see Polhill and Raven (1981), Ferguson and Tucker (1994), Crisp and Doyle (1995), Doyle and Luckow (2003), and Lewis et al. (2005: geographic distributions, illustrations, etc. of all genera); for much information about Genisteae, see Polhill (1976). For chemistry, about which a great deal is known, see e.g. Hegnauer (1994, 1996), Southon (1994), and Hegnauer and Hegnauer (2001), also Frohne and Jensen (1992) and Waterman (1994: secondary metabolites in general), Wink and Waterman (1999: evolution of secondary metabolites), Wink and Mohamed (2003: particularly useful), Dixon and Sumner (2003), and Wink (2003, 2013). For polysaccharides and flavonoids in particular, see Hegnauer and Grayer-Barkmeijer (1993) and Harborne and Baxter (1999), for gums and resins, see Lambert et al. (2009, 2013), for the synthesis of quinolizidine alkaloids (from cadaverine), see Bunsupa et al. (2012), for terpenoids, see Langenheim (1981, 2003), for seed galactomannans, etc., see Buckeridge et al. (2000b) and Meier and Reid (1982: Lupinus has galactans in its cotyledons), for alkaloids, see Aniszewski (2007), and for glucosylceramides, see Minamioka and Imai (2009). For starch, see Czaja (1978) and for epidermal wax crystals, see Ditsch et al. (1995).
For wood anatomy, see Baretta-Kuipers (1981), Gasson et al. (2000 [Faboideae], 2003, 2009 [Caesalpinieae], and references), and Evans et al. (2006: Mimosoideae), and for distinctive secondary thickening in Bauhinia, see Carlquist (2013) and Fisher and Blanco (2014). Luckow et al. (2005) discuss variation in flower and seed in Mimosoideae; for general floral and inflorescence morphology, see Endress (1994b), Naghiloo et al. (2012: variability), and Prenner (2013: Faboideae), for carpel development, van Heel (1981, 1983), van Heel (1993: Archidendron, if five carpels, alternate with corolla), Sinjushin (2014: polymerous gynoecia in peas), and Paulino et al. (2014: polycarpellary gynoecia usu. in Mimosoideae, unknown from Faboideae with keel flowers), for general floral development, also Tucker (1996a, b, 2001 [Cynometreae], 2002b, c, 2003c [all Detarieae], 2003a), Zimmerman et al. (2013: Dialinieae), Mansano and Teixeira (2008: Lecointea clade), Mansano et al. (2002: Swartzieae s.l.), Pedersoli et al. (2010: Copaifera, Detarieae), Song et al. (2011: Clianthus), Paulino et al. (2011: Indigofera, 2013: Swartzia), Bruneau et al. (2014: Detarieae), and Leite et al. (2014: Dipterygeae). For pollen morphology, see Feuer (1987), Banks and Klitgaard (2000: Detarieae), Banks and Lewis (2009), Banks et al. (2003), Kuriakose (2007), and Banks et. al. (2013, 2014: Cercideae, diverse in derived taxa), for tapetum, see Wunderlich (1954: c.f. Caesalpinia) and Buss and Lersten (1975), for embryology, etc., see Newman (1934), Dnyansagar (1970) and Guignard (1881). For floral anatomy, see Rao et al. (1958), for funicle morphology, see Endo (2012a). For cotyledon areole presence, the size of the areole being linked to the amount of endosperm, see Endo and Ohashi (1998) and Lackey (2011), for endosperm, see e.g. Rau (1953). For information about seed coat anatomy, see e.g. Pammel (1899), Corner (1976), Gunn (1981), Kirkbride and Wiersema (1997), Moïse et al. (2005), and Lackey (2009), for the pleurogram, esp. in Chamaecrista, see De-Paula and Oliveira (2008, 2012), for fruit anatomy in Crotalaria and relatives, see Le Roux et al. (2011), and for fruits and seeds in "Caesalpinoideae", see Gunn (1991); many features other than those noted in the characterisation above may be of systematic interest.
Phylogeny. The Legume Phylogeny Working Group (2013a) provide a good summary of relationships in the family. Fabaceae are monophyletic in both molecular and morphological analyses, although support may not be strong. "Caesalpinioideae" are wildly paraphyletic at the base of Fabaceae, with Mimosoideae s. str. and Faboideae being monophyletic. In addition to placing Cercideae as sister to the rest of Fabaceae, Wojciechowski et al. (2004) found that Dialiinae/Diallieae were sister to the remainder. There were then two main clades, the Mimosoideae, to which Ceratonia, Gleditsia, etc., Caesalpinieae, Cassieae, and Cercideae (all "Caesalpinioideae") are more or less successively sister taxa, and Faboideae; Bruneau et al. (2008a, b) found a somewhat similar set of relationships (see tree here). Cercis and Bauhinia may be sister to all other Fabaceae (e.g. J. J. Doyle et al. 2000 and references; Bruneau et al. 2001), although they are also placed sister to Detarieae s.l., if sometimes with only with moderate support (Wojciechowski et al. 2004; Lavin et al. 2005; Forest et al. 2007b). Detarieae include genera like Cynometra, Tamarindus and Amherstia and have also been placed by themselves as sister to all Fabaceae minus Cercideae. Duparquetia is also in this general area (Forest et al. 2002; Tucker et al. 2002), and was found to be sister to Dialiinae by Herendeen et al. (2003b). Cercideae, Duparquetia, and/or Detarieae s.l. are all candidates for being sister to the rest of the family (Bruneau et al. 2008a, b; Cardoso et al. 2012a: Duparquetia not included; Legume Phylogeny Working Group 2013a). Morphology and anatomy support this: All three lack the vestured pits that are common in the rest of the family (they are also absent in Cassieae). Duparquetia is highly derived, but although the carpel develops after the stamens are initiated, unlike other Fabaceae (Prenner & Klitgaard 2008a, esp. b), this could be plesiomorphic; the pollen is also distinctive (Banks et al. 2006).
Within Cercideae, Cercis is sister to the rest (Sinou et al. 2009). Generic limits of Bauhinia are discussed by Sinou et al. (2008, 2009); at least Bauhinia s. str. lacks the srp12 intron (Doyle et al. 1995; Lai et al. 1997) and also the rpl2 intron (Sinou et al. 2009).
Detarieae s.l. (Bruneau 2000; Mackinder 2005: genera; Léonard 1957: seedlings of African taxa, a classic study) show extensive loss of sepals and/or petals and/or stamens, and linked with the first two changes in particular, increase in size of the bracteoles and in number of the stamens (Tucker 1992b, 2000, etc.). Thus in Monopetalanthus durandii the flower is surrounded by bracteoles and the floral formula is K 1 (minute), C 1; A 10; G 1, and Brachystegia glaucescens also has large bracteoles, K 5 (all small), C 0; A 10; G 1 (Tucker 2000). Resins found in some Detarieae contain distinctive bicylic diterpenes, and may be an apomorphy for a subgroup within the tribe (Fougère-Danezan et al. 2007). Pollen is also extremely variable (Banks & Klitgaard 2000; Banks 2003). There is amyloid in the cotyledons (Hegnauer & Grayer-Barkmeijer 1993), also found in Sclerolobieae (= Tachigalieae: see Kooiman 1960; Meier & Reid 1982). Redden et al. (2010) examined relationships in the Brownea clade, possible synapomorphies for it being an unchanneled leaf rachis, thread-like stipules, connate bracteoles, four sepals, and introrse anthers.
A clade made up of the ex-caesalpinioid Dialiinae seems well supported as sister to the rest of Fabaceae; the monotypic neotropical Poeppigia is sister to the rest of Dialiinae (Bruneau et al. 2008). The inflorescence is determinate, the fruit indehiscent (drupe or samara), and floral organs are often lost - for example, Dialium guineense has small bracteoles, and a floral formula of K 5, C 1 (small), A 2, G 1 (Legume Phylogeny Working Group 2013a).
There are then two large clades. Faboideae are monophyletic, as are Mimosoideae in the old sense, but the recognition of the latter makes remaining Caesalpinioideae highly paraphyletic.
First large clade. In the [some caesalpinioids plus Mimosoideae] clade, the poorly-supported Umtiza clade is sister to the rest. The Umtiza clade includes taxa like Gleditsia, Gymnocladus and Ceratonia, several of which are dioecious and have smallish, greenish flowers sometimes with a poorly differentiated calyx and corolla - not plesiomorphic features (Herendeen et al. 2003a; Forest et al. 2007b; see also Redden & Herendeen 2006: morphological phylogenetic analysis; Fougère-Danezan et al. 2003, 2007, 2010: molecular and morphological studies; Legume Phylogeny Working Group 2013a). Other ex-caesalpinioids with small, more or less simultaneously-opening flowers borne close together (e.g. Dimorphandra) are in this area of the tree (Luckow et al. 2003; Wojciechowski 2003; Bruneau et al. 2008a, b). They show considerable similarity to Mimosoideae s. str. in wood anatomy (Evans et al. 2006) and also in pollen, which is rather homogeneous although nearly always in monads (Banks & Lewis 2009). Genera like Pentaclethra are also to be included (c.f. Bouchenak-Khelladi et al. 2010b, but some confusion there?), while taxa like Dinizia, Pachyelasma and Erythrophleum, also with racemose inflorescence and small, more or less polysymmetric flowers with free sepals and petals (and ten stamens), were in a grade immediately basal to Mimosoideae (Bouchenak-Khelladi et al. 2010b); there is a considerable amount of phylogenetic structure here (Kyalangalilwa et al. 2013). Caesalpinia, Cassia, and relatives are also basal to Mimosoideae, Dimorphandra, Peltophorum, etc. (Cardoso et al. 2012c), and some of these taxa - Caesalpinia, Cassia, Dimorphandra - have large more or less monosymmetic/asymmetric flowers. Gagnon et al. (2013) discussed relationships around the old Caesalpinia. In general, relationships between these ex-caesalpinioids remain unclear (Cardoso et al. 2012c; see also Manzanilla & Bruneau 2012; Legume Phylogeny Working Group 2013a, b).
For phylogenetic relationships within Senna, see Marazzi et al. (2006), and for relationships within Chamaecrista, see de Souza Conceição et al. (2009).
Within Mimosoideae s. str. there is a large monophyletioc clade, Mimoseae I, in which Ingeae, derived, with a valvate calyx and many stamens connate and forming a tube, are embedded in Acacieae (e.g. Clarke et al. 2000; Robinson & Harris 2000; Miller & Bayer 2000, 2001; Luckow et al. 2003; Jobson & Luckow 2007; Brown 2008; Brown et al. 2008; Bouchenak-Khelladi et al. 2010b; Miller & Seigler 2012; Kyalangalilwa et al. 2013). See Richardson et al. (2001b) for the diversification of Inga. The old Acacia subgenus Acacia, which includes the bull's horn acacias, seems to be monophyletic, but Acacia s.l. is highly poly/paraphyletic. Murphy et al. (2000, 2003, 2010 [relationships still only moderately resolved]) and Miller et al. (2003) discuss the phylogeny of Acacia s. str., the old subgenus Phyllodinae, Brown et al. (2012) focussing on relationships of the group outside Australia. Miller and Bayer (2003) looked at relationships in Vachellia, the old subgenus Acacia, and Senegalia, the old subgenus Aculeiferum (support for the monophyly of this is weak - Miller & Seigler 2012). Kyalangalilwa et al. (2013) looked at the whole complex; there may still be clades of the old Acacia without names. Siegler (2003) summarized the phytochemistry of the complex, Evans et al. (2006) detailed wood anatomy, and Kergoat et al. (2007) noted what bruchids had to say about systematics of Acacia s.l.; see also Muelleria 26(1). 2008, a special issue on Acacia, and also World Wide Wattle website. Albizzia is also in Mimoseae I, and it seems potentially quite polyphyletic (Kyalangalilwa et al. 2013). Mimosa may be monophyletic and sister to Piptadenia (Besseger et al. 2008); Simon et al. (2011) provide an extensive phylogeny of Mimosa, optimizing various characters on the tree. De Souza et al. (2013) provide a comprehensive phlyogeny of Calliandra - largely, if not entirely, New World - and its immediate relatives.
Mimoseae II, named for convenience, make a paraphyletic grade basal to Mimoseae I. They include Parkia, a polyphyletic Neptunia, Leucaena, etc., as well as genera like Pentaclethra (Kyalangalilwa et al. 2013: see also above). Catalano et al. (2008) provide a phylogeny of the ecologically important New World genus Prosopis, also in this area.
Second Large Clade, = Faboideae. The following topology (simplified) aids in the discussion of relationships in the monophyletic Faboideae: [Swartzieae, Dipterygieae, etc. [Cladrastis, etc., [(= 50 KB inversion clade) Andira et al., Vatairea et al., Lecointea et al., genistoids: GEN, [Amorpheae + dalbergioids = dalbergioids s.l.: DAL], [baphioids: BAPH [(= non-protein amino acid accumulating clade) mirbelioids: MIRB [[Indigofereae + millettioids: MILL] [robinioids: ROB + Inverted Repeat Loss Clade: IRLC]]]]]]], seems moderately well supported (Wojciechowski 2003; McMahon & Sanderson 2006; Legume Phylogeny Working Group 2013a). The [robinioids + IRLC] clade is the hologalegina clade (see Farruggia & Howard 2011 for possible nuclear markers). The tree here is based largely on Wojciechowski et al. (2004), Peters et al. (2010) and Cardoso et al. (2012c); see also the Legume Phylogeny Working Group (2013a). McMahon and Sanderson (2006) provide a supermatrix analysis of 2228 species of Faboideae.
Within Faboideae, Swartzieae, woody, nodulators, with remarkable flowers and arillate seeds, may be sister to the rest, but support is weak (Ireland et al. 2000; Pennington et al. 2000; Lavin et al. 2005). Swartzieae are largely made up of Swartzia s. str. (see Torke & Schaal 2008 for a phylogeny). Other clades in this area include Amburana and the Dipterygieae, etc., but the relationships of the clades are unclear (Cardoso et al. 2012c), also the lecointeoids (Mansano et al. 2004) and the vataireoids (Cardoso et al. 2013: leaves in groups at ends of branches). Cardoso et al. (2013) found the clade [Angylocalyceae [Dipterygeae + Amburaneae]] to be sister to the rest of Faboideae, although this position must be confirmed; they also discussed other relationships among Faboideae basal to the non-protein amino acid clade.
50 KB inversion clade.
GEN: Crisp et al. (2000) outline relationships in Genisteae s.l., with their distinctive quinolizidine alkaloids (see also van Wyk 2003 for chemistry). For relationships within Crotalarieae, see Boatwright et al. (2008b, esp. c) and of Lotononis and relatives in particular, Boatwright et al. (2011: also character evolution). Le Roux et al. (2013) found little support for relationships along the backbone of Crotalaria, although several well-supported clades were recovered. For relationships within Psoraleae, see Egan and Crandall (2008), and in Canary Island Genisteae, see Percy and Cronk (2002), for diversification in Cape genistoids, see Edwards and Hawkins (2007); for relationships in Ononis, see Liston (1995), and Cytisus, Cubas et al. (2002).
DAL: For the phylogeny of dalbergioid legumes, see Lavin et al. (2000); desmodioid nodules, small oblate nodules of determinate growth that are always associated with a lateral root, are common here (Lavin et al. 2001). The large genus Machaerium is more related to Aeschynomene section Ochopodium (that genus is polyphyletic) than to Dalbergia, so the apparent similarities in habit, fruit, etc., between Machaerium and Dalbergia need re-evaluating (Ribeiro et al. 2007; Chaintreuil et al. 2013). Cardoso et al. (2012a, b) and Klitgård et al. (2013) noted that taxa with polysymmetric flowers have evolved several times in this clade and may nestle within genera with papilionoid flowers (e.g. Klitgård et al. 2013). For relationships within Amorpheae and the floral evolution of the latter (petals may be lost, or all look rather similar; a stemonozone may be developed; etc.), see McMahon and Hufford (2002, 2004, 2005) and McMahon (2005). For relationships in Arachis, see Krapovickas and Gregory (2007).
MIRB: For relationships in or revisions of Mirbelia s.l., see Crisp and Cook (2003a, b), Gastrolobium, Chandler et al. (2001), Pultenaea, Orthia et al. (2005), and Jacksonia, Chappill et al. (2007).
MILL: The crown age of this clade is estimated at around 44.3 m.y. (H. Li et al. 2013) or (51.5-)48.5(-42.3) m.y. (Sirichamorn et al. 2014a). Members of the millettioid clade have a pseudoracemose inflorescence with more than a single flower at each node (Tucker 1987a); see da Sila (2012) for a phylogeny of part of this clade, Lonchocarpus is split. [Milletieae + Indigofereae] may share early expression of monosymmetry in floral development (Paulino et al. 2011). For the delimitation of Millettieae, see Lavin et al. (1998); Hu (2000) and Hu et al. (2000) studied their phylogeny, and Abrus (with nine stamens) is (near-)basal (Prenner 2013b and references). Kajita et al. (2001: rbcL) also looked at the phylogeny of Millettieae and relatives. For the phylogeny of Derris and its immediate relatives, see Sirichamorn et al. (2012, 2014a, b).
Indigofereae have true racemes (Wojciechowski et al. 2004). Barker et al. (2000) and Schrire et al. (2009) disentangle relationships within Indigofereae, finding considerable phylogenetic structure (i.a. there are four major clades within Indigofera) that can be linked with both morphology and ecology. Stefanovic et al. (2009: eight chloroplast genes) concentrated on relationships among the some 2,000 species of phaseoloids, finding substantial resolution, i.a. that Mucuna was sister to Desmodium and its relatives, and the combined clade was sister to the rest of the group, which also includes Cajanus, Vigna, Erythrina, etc. (see also H. Li et al. 2013 for a more detailed analysis of Phaseoleae-Phaseolineae, ¾ genera included). For a phylogeny of Phaseolus itself, see Delgado-Salinas et al. (1999, 2006); Vigna has to be dismembered (Delgado-Salinas et al. 2011). Thompson et al. (2001) looked at relationships within Brongniartieae, members of which are Australian-South American. The pantropical Erythrina is not monophyletic (de Moura et al. 2011).
ROB: For the phylogeny of Robinia and its relatives, which include Lotus and Sesbania, two genera that are quite close, see Wojciechowski et al. (2000), Lavin et al. (2003), and Farruggia and Wojciechowski (2009), and of Canary Island Loteae, see Allan et al. (2004).
Wojciechowski et al. (2000) outlined relationships in this speciose clade. Extensive phylogenetic studies (e.g. Wojciechowski 1993, 2004; Wojciechowski et al. 1999; Kasempour Osaloo et al. 2004; Scherson et al. 2004) show that Astragalus is monophyletic; most New World taxa are aneuploid (n = 11-15) and are also monophyletic, other species are base 8; for relationships in Old World Astragalus, see Kasempour Osaloo et al. (2004), Kazemi et al. (2009) and Riahi et al. (2011). Oxytropis is sister to Astragalus; for some relationships in the former, see Archambault and Strömvik (2012). Safaei Chaei Kar et al. (2014) looked at relationships within Onobrychis;; current infrageneric groupings had little support. For the phylogeny and diversification of Caragana in the context of the Qinghai-Tibetan Plateau uplift, see Zhang et al. (2009) and Zhang and Fritsch (2010). Within Trifolium the American species form a monophyletic group (Ellison et al. 2006; Liston et al. 2006). Phylogenetic relationships within Medicago have turned out to be highly reticulating (Maureira-Butler et al. 2008); Medicago probably includes Trigonella, and for its limits, see Bena (2001) and Steele et al. (2010). A preliminary phylogeny of Lathyrus suggested that the ca 20 South American species might represent a single clade derived from Northern hemisphere ancestors (Asmussen & Liston 1998; see also Kenicer et al. 2005). Within Hedysareae Alhagi may be sister to the rest (Amirahmadi et al. 2014).
Classification. See the Legume Phylogeny Working Group (2013b) for a fascinating introduction to the dynamics of the reclassification of the family; because relationships at the deeper nodes are poorly known, one must expect changes in the names for the major elements that make up the scaffolding of the family.
In general, a fair bit of adjustment to generic limits is needed, but in some situations, although it is clear that changes are needed, sampling is not good enough to know exactly what to do (e.g. see Percy & Cronk 2002; Allan et al. 2004; Ribeiro et al. 2007; Cardoso et al. 2012a; Gagnon et al. 2013). For generic limits in Cercideae, see Wunderlin (2010), for those around Gastrolobium, see Chandler et al. (2001), for those around Vigna, see Delgado-Salinas et al. (2011), for those around Lotononis, see Boatwright et al. (2011), for those around Calliandra, see de Souza et al. (2013), and for those around Caesalpinia, see Gagnon et al. (2013); the limits of Derris have been redrawn (Sirichamorn et al. 2014b). Unique combinations of floral characters can be used to recognize genera around Crotalaria (Le Roux & van Wyk 2012).
The old Acacia subgenus Acacia, which includes the bull's horn acacias, seems to be monophyletic, but Acacia s.l. is polyphyletic. As Maslin (2001) noted sadly of the 955 or so species then placed in Acacia for the Flora of Australia treatment, "we are obliged to present the flora treatment [i.e., everything in the one genus] in the absence of a more meaningful classification". However, things are changing (Maslin et al. 2003) - the argument now is over what names to call the bits into which Acacia s.l. is to be divided (see above). See Miller and Bayer (2003) for Vachellia, the old subgenus Acacia, and Senegalia, the old subgenus Aculeiferum; see also Siegler et al. (2006) for the American segregate Mariosousa. However, some remain deeply unsatisified with this nomenclatural solution.
See Pennington (1997) for a monograph of Inga and Dexter et al. (2010) for some species limits there. For a sectional classification of the neotropical Swartzia (Faboideae), see Torke and Mansano (2009), and for that of the pantropical Crotalaria, see le Roux et al. (2013). Thompson (2001) provides a careful study of E. Australian Hovea (Brongniartieae).
Previous Relationships. Fabaceae s.l. have often been placed in their own order, as in both Cronquist (1981) and Takhtajan (1997), and then they are usually divided into three families, Fabaceae/Leguminosae, Caesalpiniaceae and Mimosaceae. They can be confused with Connaraceae (Oxalidales), although the latter lack stipules, their flowers are polysymmetric and have stamens of two distinctly different lengths, and their gynoecium is frequently multicarpellate. However, in both the RP122 chloroplast gene has moved to the nucleus, and the ovaries of both have adaxial furrows (c.f. the ventral slit: Matthews & Endress 2002). Fabaceae have also been linked with Sapindaceae (e.g. Dickison 1981b), here in the malvids, but there is little support other than the common possession of compound leaves and non-protein amino acids for such an association.
Botanical Trivia. There has been as much diversification of the ycf4 protein, involved in photosystem 1 assembly, within Lathyrus as there has been between cyanobacteria and other angiosperms (Magee et al. 2010).
The seeds of Mora megistosperma (Caesalpinieae) are, at ca 18 x 12 cm, perhaps the largest of any broad-leaved angiosperm (Lewis et al. 2005).
[Surianaceae + Polygalaceae]: ?
Age. This node is dated to (71-)68, 66(-63) m.y.o. (Wikström et al. 2001).
SURIANACEAE Arnott, nom. cons. Back to Fabales
Woody; ellagic acid?; cork also in inner cortex; storying +/0; wood fluorescing?; vessels in radial multiples; (sieve tube plastids with starch grains and protein filaments forming a peripheral shell); nodes 3:3 (1:1 - Suriana); (medullary vascular bundles - Recchia); sclereids +; petiole bundle arcuate to annular; leaves spiral or two-ranked, (unifacial; pinnate, leaflets alternate, articulated), (stipules 0 - Suriana); inflorescence cymose, usu. terminal; pedicels articulated; K connate basally or not, quincuncial, C (0), contorted, shortly clawed or not; ?receptacular tissue ± forming a ring around the C base; A obdiplostemonous (= and opposite sepals); pollen surface variable (vermiform - Cadellia); nectary 0; (gynophore +, nectariferous - Recchia); G 1-5, when 5 opposite C, styluli separate, ± gynobasic, stigma clavate to capitate; ovules surrounded by mucilage, 1-5/carpel, apotropous [Suriana], campylotropous to amphitropous, unitegmic, integument 3-7 cells across, parietal tissue 4-5 cells across, (nucellar cap +), hypostase +; megaspore mother cells several, antipodal cells ± degenerate; fruit a berry, drupe or nut, endocarp with outer layer of palisade sclereids, other cells apart from the inner epidermis isodiametric, K persistent, accrescent or not; exotestal cells enlarged, cuboidal, tanniniferous, rest crushed [ca 7 cells thick], or seed tegmic; chalazal endosperm haustorium +, endosperm 0, embryo green, curved or folded, cotyledons incumbent; n = ?; germination epigeal, phanerocotylar.
5[list]/8 Mostly Australian, also Mexico (Recchia), pantropical (Suriana maritima) (map: from van Steenis & van Balgooy 1966 [blue - Suriana maritima]; FloraBase xi.2010). [Photo - Flower.]
Age. Crown-group Surianaceae are some (50.4-)38.7(-27.0) m.y. old (Bello et al. 2009).
Chemistry, Morphology, etc. The family is vegetatively rather heterogeneous, although its wood anatomy is quite homogeneous (Webber 1936). The exotesta of Suriana is described as being green (Rao 1970). Both Cadellia and Recchia have thickened cell walls in the exocarp and sclereids in their bark parenchyma (Crayn et al. 1995).
For more information, see Gutzwiller (1961) and Weberling et al. (1980), and Schneider (2006), all general, Hegnauer (1973, as Simaroubaceae), chemistry, Jadin (1901) and Boas (1913), both vegetative anatomy, Mauritzon (1939), Wiger (1935), Anantaswamy Rau (1940a), Rao (1970) and Heo and Tobe (1994), all embryology, etc., Gadek and Quinn (1992: pericarp); for floral development, see Bello et al. (2007/8: Suriana only). Additional data from: Cadellia - Benson s.n. = NSW 408528 (anatomy); Stylobasium - Latz 12864 (fruit), Strid 20708 (anatomy).
The vegetatively "atypical" Suriana is the only genus whose embryology has been studied and Surianaceae as a whole are little known chemically.
Phylogeny. [[Recchia + Lundellia] [Suriana [Cadellia + Stylobasium]] are suggested relationships in the family (Forest et al. 2007b); c.f. also Crayn et al. (1995) and Bello et al. (2009).
Classification. Although the sieve tube plastids of Stylobasium are distinctive, having sieve starch grains and protein filaments forming a peripheral shell (Behnke et al. 1996), there seems little reason to recognise Stylobasiaceae as a family, i.a. four families for five genera would then be needed.
Previous Relationships. Surianaceae were included in Rosales-Simaroubaceae (here in Sapindales) by Cronquist (1981) and in Rutales as a separate family by Takhtajan (1997).
Synonymy: Stylobasiaceae J. Agardh
POLYGALACEAE Hoffmannsegg & Link, nom. cons. Back to Fabales
Saponins +; nodes 1:1; styloids 0; (tracheidal idioblasts +); (stomata other than anomocytic); plant glabrous or with unicellular hairs; branching from previous flush; axillary buds 2 or more; lamina entire, often paired glands [crateriform extrafloral nectaries] or thorns at nodes (elsewhere); flowers monosymmetric, ± keeled; K quincuncial, C 5, keel ± apparent, (not clawed); A 8, ± connate, basally adnate to C, median adaxial A often absent; pollen polycolporate, surface psilate or foveolate; (disc excentric); G connate, style long, stigma dry; micropyle zigzag (endo-, exostomal), exostome often long, outer integument 2-5 cells across, inner integument (1-)2(-3) cells across, parietal tissue 2-3 cells across, nucellar cap ca 3 cells across, suprachalazal region ± massive; fruit a berry; testa multiplicative, exotesta subsclerotic or otherwise distinct, endotestal cells ± palisade, U-thickened, crystalliferous; endosperm copious or not, ± starchy; rpl22 gene transferred from chloroplast to nucleus [?sampling].
Ca 21 [list]/965 - four tribes below. World-wide, except the Arctic and New Zealand. [Photo - Flower.]
Age. Diversification of Polygalaceae began in the Tertiary (65.5-)57.4(-49.3) m.y.a. (Bello et al. 2009).
1. Xanthophylleae Chodat
Shrubs or trees; growth sympodial, terminal bud aborts; plants Al-accumulators; wood parenchyma apotracheal, diffuse; glands at nodes, (conspicuous domatia on leaf blades); inflorescence indeterminate; K unequal, C contorted, (no keel), (adaxial petals with colour patterning); A (7-10); G , placentation parietal, stigma small, bilobed (capitate); ovules 2-8(-20)/carpel, apotropous, in two rows, outer integument 4-12 cells across; (fruit irregularly loculicidally dehiscent), K deciduous; testa strongly multiplicative, vascularized; hypostase massive; n = ?
1/95. Indo-Malesia (map: from van der Meijden 1982).
Synonymy: Xanthophyllaceae Reveal & Hoogland
[Polygaleae, Carpolobieae, Moutabeae]: inflorescence cymose; A often monadelphous, anthers opening apically [pores/slits]; 1 ovule/carpel; seed hairy (glabrous), exostomal/funicular aril + (0).
More or less world-wide (Map: from Wickens 1976; Frankenberg & Klaus 1980; Trop. Afr. Fl. Pl. Ecol. Distr. 1. 2003; GBIF 2009; Flora of China; Australia's Virtual Herbarium xii.2012; orange from Paiva 1998).
2. Polygaleae Chodat
Herbs (echlorophyllous myco-heterotrophs), lianes, shrubs; (ergoline alkaloids +), at least some smell of wintergreen, tannins 0 [Polygala]; (successive cambia +); pits vestured; banded paratracheal parenchyma +; (glands at nodes); (2 abaxial lateral K, minute), two adaxial lateral K = wings, two connate adaxial C = the standard, abaxial C = the keel, often fringed [with crest], 2 abaxial-lateral C minute; (A 2-7), anthers with apical pores; G  (adaxial member suppressed), stylar canal + [Polygala], stigma bilobed, ± asymmetric; (postament - Epirrhizanthes?); fruit an often flattened capsule, drupe or samara, (K persistent, green - Polygala, etc.); hilar/chalazal elaiosome + (0); testa ?multiplicative; n = 6+, very variable.
18/830: Polygala (?350), Monnina (180), Muraltia (120), Securidaca (80). World-wide, except the Arctic and New Zealand (Map: from Wickens 1976; Frankenberg & Klaus 1980; Trop. Afr. Fl. Pl. Ecol. Distr. 1. 2003; GBIF 2009; Flora of China; Australia's Virtual Herbarium xii.2012; orange from Paiva 1998).
Age. The [Polygala + Securidaca] node is estimated to be (42-)40, 28(-26) m.y.o. (Wikström et al. 2001).
The distinctive Paleosecuridaca curtisii, from the Late Palaeocene of North Dakota ca 60 m.y.a., has fruits remarkably like those of Securidaca and seeds with a testa that has a well developed palisade layer, however, there are two seeds per carpel (Pigg et al. 2008b).
3. Carpolobieae Eriksen
Shrub to small tree, liane; (glands at nodes); (C contorted); A (4) 5, anthers with short confluent apical slits; G , stigma capitate; exotesta fleshy [?both]; n = 9-11.
2/6. Tropical Africa.
4. Moutabeae Chodat
Woody, (lianes); plants Al-accumulators; successive cambia +; banded apotracheal parenchyma +; petiole bundle annular, with wing bundles; glands on leaves (and at nodes); inflorescence often racemose; K adnate to C, abaxial C not keeled; A (6-10), anthers with short confluent apical slits; G [3-8], stigma capitate; funicular aril +; n = 14.
4/15. Tropical America, New Guinea to New Caledonia. [Photos - Flowers, Flower - Close-up, Petioles, Branch, Petioles with ants, Flower with moth]
Synonymy: Diclidantheraceae J. Agardh, Moutabeaceae Pfeiffer
Evolution. Divergence & Distribution. The evolution of elaiosomes in Polygalaceae is dated to (69.9-)54-50.5(-35.2) m.y.a., well after that of the ant clades concerned, and it may have spurred diversification in the family (Forest et al. 2007b). Muraltia, also myrmecochorous and with some 120 species found mostly in the Cape region of South Africa, may have diversified quite recently, mostly within the last ca 10 m.y. (Forest et al. 2007a); Verboom et al. (2009) thought diversification started in the Fynbos (21.4-)18.5(-14.1) m.y.a. and in the Succulent Karoo (4-)2.5(-1.3) m.y.a.
Bello et al. (2012) list a number of apomorphies for the family and of several clades within it.
Ecology & Physiology. Xanthophyllum is one of the five most speciose genera in West Malesian l.t.r.f. (Davies et al. 2005).
The myco-heterotrophic Epirixanthes is presumably asociated with glomeromycote fungi, one of the few examples of a myco-heterotrophic broad-leaved angiosperm with this kind of fungal association.
Pollination Biology & Seed Dispersal. The flower in Polygalaceae is quite differently constructed from that of Fabaceae (Westerkamp & Weber 1999; Bello et al. 2010, but see Prenner 2004d), although quite often both looking and being functionally similar. Note that the flowers of Polygala, which in overall appearance are particularly like those of some Fabaceae, do not represent the plesiomorphic condition of Polygalaceae; overall floral variation in Polygalaceae is considerable.
In at least some North American species of Polygala pollen is presented on the sterile lobes of the asymmetric stigma (secondary pollen presentation: Weekley & Brothers 1996; see Castro et al. 2008a for details; Bello et al. 2010 for details of stigma morphology).
Ant dispersal is quite common in Polygaleae, and hilar/chalazal elaiosomes (the former are called caruncles) may be an apomorphy here, although there may have been more than one gain (and loss) of these features (Forest et al. 2007b; Lengyel et al. 2009, 2010 for myrmecochory).
Bacterial/Fungal Associations. Epirixanthes is an echlorophyllous myco-heterotroph.
Vegetative Variation. Although genera like Xanthophyllum and some Moutabeae may have paired glands at the nodes, other genera seem to lack anything even faintly like stipules, and where stipules might be lost in this part of the tree is uncertain. De Aguiar-Dias et al. (2011) have recently suggested that the paired nectary glands at the base of the leaf in Polygala laureola are indeed stipules because they receive a vascular bundle from the single foliar vascular trace.
Chemistry, Morphology, etc. Polygala myrtifolia has eight stamens; the two stamens in the median plane, so on opposite sides of the flower, appear to have been lost (Prenner 2004d); see Bello et al. (2010) for other floral diagrams. The degree of connation of the filaments varies, as does that of their sometimes rather slight adnation to the petals. For floral morphology and development of Polygaleae, see Krüger and Robbertse (1988) and Krüger et al. (1988), and for that of the family as a whole, see Bello et al. (2010, 2012). The tricolpate pollen of Balgooya is probably derived; some Polygalaceae such as Heterosamara have asymmetric, almost boat-shaped pollen grains (Banks et al. 2008). Some species of Polygala, at least, have a stylar canal (Castro et al. 2008b). Monnina seems to have a nucellar cap ca 6 cells across, while the inner integument of Securidaca is up to 9 cells across in the endostomal region (Verkeke 1985).
Additional information is taken from Eriksen (1993a) and especially from Eriksen and Persson (2006), both general. For chemistry, see Hegnauer (1969, 1990), for wood and leaf anatomy of Moutabeae, see Styer (1977), also Verkeke (1984, 1991) and Takhtajan (2000), all ovule and seed and Banks et al. (2008: pollen morphology and evolution). Also see Johow (1910: Epirrhizanthes), Paiva (1998: Polygala, especially Africa and Madagascar), for a monograph of Xanthophyllum, van der Meijden (1982), and for the Polygalaceae website see Freire-Fierro (2001 onwards).
Phylogeny. Of the four groups mentioned above, Moutabeae may be paraphyletic (Persson 2001: trnL-F), although adding rbcL data suggests they are monophyletic (Forest, in Eriksen & Persson 2006), and morphology points in this direction (Eriksen 1993b); the other three groups appear to be monophyletic (although Carpolobieae are only weakly supported). However, all four tribes are strongly supported in a three-gene analysis (Forest et al. 2007b), and Xanthophylleae are sister to the other three tribes; relationships between the three were unclear and remain so in Bello et al. (2012). Polygala and Bredemeyera are grossly paraphyletic (Persson 2001). See Eriksen (1993b) for a morphological phylogeny.
Classification. Abbott (2011) split Polygala in the North American flora, and the dismemberment of the genus proceeds apace (see Abbott et al. 2013).
Previous Relationships. The Polygalales of Cronquist (1981) included seven families, the mutual affinities of five of which were described as being "widely acce pted". These include Xanthophyllaceae (= Polygalaceae), Vochysiaceae (Myrtales), Trigoniaceae (Malpighiales) and Tremandraceae (= Elaeocarpaceae, Oxalidales). For Emblingiaceae, often included in (e.g. Cronquist 1981; Mabberley 1997) or near (e.g. Takhtajan 1997) Polygalaceae, see Brassicales.