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 stele with xylem and phloem originating on alternate radii, not medullated [no pith], 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).
MONOCOTYLEDONS / MONOCOTYLEDONEAE / LILIANAE Takhtajan
Plant herbaceous, perennial, rhizomatous, growth sympodial; non-hydrolyzable tannins [(ent-)epicatechin-4] +, neolignans, benzylisoquinoline alkaloids 0, hemicelluloses as xylans; root apical meristem?; root epidermis developed from outer layer of cortex; trichoblasts in atrichoblast [larger cell]/trichoblast cell pairs, the former further from apical meristem, in vertical files; endodermal cells with U-shaped thickenings; cork cambium in root [uncommon] superficial; stele oligo- to polyarch, < class="apo">medullated [with prominent pith], lateral roots arise opposite phloem poles; primary thickening meristem +; vascular bundles in stem scattered, (amphivasal), vascular cambium 0 [bundles closed]; tension wood 0; vessel elements in root with scalariform and/or simple perforations; tracheids only in stems and leaves; sieve tube plastids with cuneate protein crystals alone; stomata parallel to the long axis of the leaf, in lines; prophyll single, adaxial; leaf blade linear, main venation parallel, the veins joining successively from the outside at the apex, transverse veinlets +, unbranched [leaf blade characters: ?level], vein/veinlet endings not free, margins entire, Vorläuferspitze +, base broad, ensheathing the stem, sheath open, petiole 0, colleters + ["intravaginal squamules"]; inflorescence terminal, racemose; flowers 3-merous [6-radiate to the pollinator], polysymmetric, pentacyclic; P = T, each with three traces, median T of outer whorl abaxial, aestivation open, members of whorls alternating, [pseudomonocyclic, each T member forming a sector of any tube]; stamens = and opposite each T member [primordia often associated, and/or A vascularized from tepal trace], anther and filament more or less sharply distinguished, anthers subbasifixed, endothecium from outer secondary parietal cell layer, inner secondary parietal cell layer dividing; G , with congenital intercarpellary fusion, opposite outer tepals [thus median member abaxial], placentation axile; ovule with outer integument often largely dermal in origin, parietal tissue 1 cell across; antipodal cells persistent, proliferating; fruit a loculicidal capsule; seed testal; embryo long, cylindrical, cotyledon 1, apparently terminal, with a closed sheath, unifacial [hyperphyllar], both assimilating and haustorial, plumule apparently lateral; primary root unbranched, not very well developed, stem-borne roots numerous, hypocotyl short, (collar rhizoids +); no dark reversion Pfr → Pr; duplication producing monocot LOFSEP and FUL3 genes [latter duplication of AP1/FUL gene], PHYE gene lost.
[ALISMATALES [PETROSAVIALES [[DIOSCOREALES + PANDANALES] [LILIALES [ASPARAGALES + COMMELINIDS]]]]]: ethereal oils 0; raphides + (druses 0); leaf blade vernation supervolute-curved or variants, (margins with teeth, teeth spiny); endothecium develops directly from undivided outer secondary parietal cells; tectum reticulate with finer sculpture at the ends of the grain, endexine 0; (septal nectaries + [intercarpellary fusion postgenital]).
[PETROSAVIALES [[DIOSCOREALES + PANDANALES] [LILIALES [ASPARAGALES + COMMELINIDS]]]]: cyanogenic glycosides uncommon; starch grains simple, amylophobic; leaf blade developing basipetally from hyperphyll/hypophyll junction; epidermis with bulliform cells [?level]; stomata anomocytic, (cuticular waxes as parallel platelets); colleters 0.
[[DIOSCOREALES + PANDANALES] [LILIALES [ASPARAGALES + COMMELINIDS]]]: nucellar cap 0; endosperm nuclear [but variation in most orders].
[LILIALES [ASPARAGALES + COMMELINIDS]]: (inflorescence branches cymose).
ASPARAGALES + COMMELINIDS: style long.
COMMELINIDS Back to Main Tree
Unlignified cell walls fluorescing blue under UV, green with NH3 [ferulic acid ester-linked]; (vessels in stem and leaves); SiO2 bodies +, in leaf bundle sheaths; stomata para- or tetracytic, (cuticular waxes as aggregated rodlets [looking like a scallop of butter]); inflorescence branches determinate, peduncle bracteate; P = K + C, bicyclic [stamens adnate to/inside corolla/inner whorl only]; pollen starchy; embryo short, broad.
Age. Estimates of the time when divergence began within commelinids are ca 120 m.y.a. (Janssen & Bremer 2004), (104-)99, 91(-86) m.y. (Wikström et al. 2001), or ca 116 m.y. (Bremer 2000b). Wikström et al. (2001) suggest an age of (104-)99, 91(-86) m.y., Magallón and Castillo (2009: relaxed and constrained penalized likelihood datings) estimate ages of ca 128 and 115 m.y., Bell et al. (2010) ages of (113-)103, 96(-86) m.y., and Magallón et al. (2013) an age of around 83.4 m.y.. Finally, estimates are (122-)116(-94) m.y. in Merckx et al. (2008a: but Dasypogonaceae sister to Arecaceae?), only ca 67.1 or 64.5 m.y. in Xue et al. (2012: note topology), 93-90 m.y. in Mennes et al. (2013) and around 106 or 83 m.y. in S. Chen et al. (2013).
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. Ecology & Physiology. Silica, an apomorphy for the commelinids, is an important plant defence, causing mechanical damage to mouthparts of would-be grazers and also having a number of physiological effects. For discussion on the effects of silica and silica bodies on herbivores, see Poaceae; most of the experimental work on this subject has been carried out on grasses.
The element silicon is important ecologically in other ways. There is a negative correlation between leaf longevity and silicon concentration in plant tissues (Cooke & Leishman 2011b). Hardly surprisingly silicon concentrations in tissues of commelinids are generally high, although less so in those commelinids that do not have SiO2 bodies (Ma & Takahashi 2002; Hudson et al. 2005).
Plant-Animal Interactions. Larval food plants of Satyrinae (Nymphalidae) butterflies, "browns", are widely distributed in the commelinids (Ehrlich & Raven 1964; Peña & Wahlberg 2008). Basal clades in Satyrinae feed on BLAs, while larvae of other clades eat monocots, especially commelinids (and within commelinids, especially Poaceae); Amathusiini seem to be the only satyrines that use a variety of non-commelinid monocot hosts (Peña & Wahlberg 2008; see also Peña et al. 2011). Unfortunately, the sister group of Satyrinae is unclear (Heikkilä et al. 2011).
Beetles of the Chrysomelidae-Hispinae+Cassidinae group are also common on commelinids (Jolivet 1988; Schmitt 1988; Vencl & Morton 1999; Chaboo 2007). 14/39 tribes of Hispinae+Cassidinae for which there is at least some larval host plant data are found on commelinids, 26/39 on some monocot or other (Chaboo 2007); the beetle larvae eat between the veins. Among the core eudicots larvae are mostly found on Boraginaceae, Solanaceae, Convolvulaceae and Asteraceae - asterids are particularly favoured. However, it is unclear if Criocerinae are in a clade immediately related to Donaciinae/Hispinae and related monocot-eating beetles, or not; the latter situation seems more likely (check Chaboo 2007; c.f. Wilf et al. 2000; Gómez-Zurita et al. 2007); Gómez-Zurita et al. (2007) found that hispines, including cassidines, were widely separated from Donaciinae, the latter being part of the [Criocerinae [Bruchinae + Donaciinae]] clade. Furthermore, feeding patterns in fossil material that look as if they were the result of the activities of hispines cannot easily be ascribed to their activities, as García-Robledo and Staines (2008) noted.
Genes & Genomes. The rate of molecular evolution in commelinids is generally high, ca 0.003 substitutions/site/m.y. (Smith & Donoghue 2008). However, in genes like ndhF, at least, the rate is similar to that in Asparagales, etc. (Givnish et al. 2006). Although genes in all three genomic compartments apparently evolve slowly in Arecaceae (Wilson et al. 1990; Baker et al. 2000a, 2000b), the rate seems similar to that in a number of other monocots other than commelinids (S. W. Graham et al. 2006). Was there an increase in the rate of molecular evolution within commelinids, some Poales being spectacular examples?
A genome duplication was common to all commelinids examined, perhaps to be pegged to monocots as a whole (Jiao et al. 2014).
Chemistry, Morphology, etc. Lignins from Poaceae and Arecaceae (and elsewhere?) have p-coumaryl alcohol as well as coniferyl and sinapyl monomers (Seigler 1998); for the synthesis of lignins from hydroxycinnamyl alcohols, which can act as the lignin monomers p-coumarate, ferulate and sinapate units, see Ralph (2009). For the chemistry of the distinctive epicuticular waxes scattered in this area of the monocots (Barthlott & Fröhlich 1983), see Meusel et al. (1994), and for cell wall ferulates, almost entirely restricted to this clade, see Harris and Hartley (1980) and Rudall and Caddick (1994).
Although vessels in the stem and leaves are common (Wagner 1977), this does not appear to be a synapomorphy. For distinctive seive tubes, see Botha (2013).
The perianth may quite sharply differentiated into a calyx and corolla, or both whorls may be petal-like, but in either case the inner whorl completely surrounds the floral apex and the stamens are borne inside it. In some of the few other monocots studied, development may be somewhat different. For floral development, see Endress (1995b) in part. In those few commelinids where floral developmental genes have been studied in detail, expression of the B-class gene orthogue of PISTILLATA seems to be restricted to the stamens/staminode and petals (Adam et al. 2007); this may be connected with the more fully bicyclic nature of the perianth in most commelinids. Starch-containing pollen is common, but has not been found in Hanguanaceae or Dasypogonaceae (only one species of the latter examined) and in some species of Haemodoraceae, Bromeliaceae, etc. Broad embryos may be a synapomorphy at about this level.
Some morphological information about the commelinids is summarized by Givnish et al. (1999).
Phylogeny. The commelinid clade is well supported in molecular studies (e.g. S. W. Graham et al. 2006, and references), and they have morphological support as well, but support for relationships between the main groups has quite often been weak (Chase et al. 2000a; Soltis et al. 2007a). Arecaceae are sister to the rest of the clade (but see below), andhe clade [Commelinales + Zingiberales] is more or less well supported (Chase et al. 2006; Givnish et al. 2006, 2010b; Soltis et al. 2007a), and with Poales sister to this clade, also by Qiu et al. (2010: mitochondrial genes; Davis et al. 2013; S. Chen et al. 2013; Ruhfel et al. 2014: chloroplast genomes). Hilu et al. (2003: matK) suggested that Poales might be sister to other commelinids, as did Soltis et al. (2011: Kingia, etc. not included), but in both cases support was weak, as was that for the position of Arecales as sister to remaining commelinids in the latter study. Arecales were weakly supported as sister to Poales in some analyses (e.g. S. W. Graham et al. 2006; Givnish et al. 2010b, maximum parsimony).
The position of Dasypogonaceae was unclear. Neyland (2002b: 26s rDNA) found Dasypogonaceae to be strongly associated with Restionaceae and other families (Poales), but this particular relationship has not been recovered in other molecular or morphological analyses. Multi-gene analyses did not link Dasypogonaceae with Arecales, even if where they ended up had no strong support (see Givnish et al. 2006 and Chase et al. 2006: near Poales; S. W. Graham et al. 2006: near [Commelinales + Zingiberales]). More recently, Givnish et al. (2011b) and Davis et al. (2011: structural mutations; see also Barrett & Davis 2011; Barrett et al. 2012a, esp. b, 2013; Ruhfel et al. 2014) have found some support in various analyses of plastomes for a position sister to Arecaceae, consistent with what morphological data there is, although in some analyses they were placed sister to [Commelinales + Zingiberales], if with little support. In a tree based on the work of Givnish et al., Carlquist (2012a) showed the relationships [[Arecales [Commelinales + Zingiberales]] [Dasyopogonales + Poales]], while Rudall and Conran (2012) were inclined to think Dasypogonaceae might be included in Poales, partly because both have epidermal silica bodies, and they might be close to Rapateaceae in particular. Indeed, alternative topologies remained possible in some analyses in Barrett et al. (2013), and these include completely novel relationships.
However, analyses of full plastid genomes suggest the relationships [[Dasypogonaceae + Arecaceae] [Poales [Commelinales + Zingiberales]]] (Barrett et al. 2012a, esp. b, 2013), those long followed here... See also Commelinales, Zingiberales, and Poales for further discussion of relationships in commelinid clades; for general relationships in monocots, see Petrosaviales and Acorales.
Classification. Givnish et al. (1999) erected a classification of four superorders and 10 orders for the commelinids based on a rbcL phylogeny. A.P.G. III (2009) recognises four orders; these are well supported clades with stable contents, Dasypogonaceae being the only family of uncertain position.
[Dasypogonaceae + Arecaceae]: septal nectaries +; ovule 1/carpel, basal, erect, outer integument usu. 6< cells across; fruit indehiscent.
DASYPOGONACEAE Dumortier Back to Main Tree.
Plant non-mycorrhizal; (extensive primary thickening +); vessels only in roots; 2 peripheral phloem strands in foliar bundles; raphides 0 [in vegetative plant]; SiO2 bodies epidermal, stomata anomocytic; leaves spiral, isobifacial, (margin serrulate), sheath well developed, bases persisting; P = T, T dry; A ± adnate to base of T; ovule epitropous[?], micropyle bistomal (zig-zag), outer integument 6-8 cells across, parietal tissue ca 2 cells across, nucellar cap ca 2 cells across; T persistent; seeds rounded, testa pale yellow; endosperm type?
4[list]/16 - two groups below. West Australia, Victoria. [Photo - Habit, Flowers].
Age. The age of crown group Dasypogonaceae is estimated at ca 100 m.y. (Janssen & Bremer 2004).
1. Dasypogoneae Engler
Stem erect, woody, or plant rhizomatous, or with stilt roots; (chelidonic acid + - Dasypogon); SiO2 bodies sand-like; hairs branched; raphides only in flowers; stomatal accessory cell ontogeny odd; bundle girders 0, three vascular bundles in a group surrounded by lignified tissue; (leaves bifacial); inflorescence axillary, capitate and scapose, or flower single; T, or outer whorl only, connate, tube short; (anthers centrifixed, dehiscing by pores - Calectasia); (G unilocular, septal nectaries 0 - Calectasia); storage nucellus massive, starchy; tegmen collapsing; n = 7, 9; cotyledon not photosynthetic, mesocotyl and coleoptile +.
2/14. S.W. Australia; South Australia/Victoria (map: from Barrett & Dixon 2001; FloraBase 2004).
Age. The two genera may have diverged some (62-)42, 38(-19) m.y.a. (Bell et al. 2010) or 49-41 m.y.a. (Wikström et al. 2001).
Synonymy: Calectasiaceae Endlicher
2. Kingieae Horaninow
Stem erect, growth monopodial and with epicortical roots [Kingia], or subrhizomatous; SiO2 bodies druse-like; substomatal cells distinctive; leaf bundle girders + [originating in mesophyll]; inflorescence axillary, with inflorescence bracts, capitate, surrounded by bracts [Kingia, or flower single, terminal; flower large [Baxteria, ca 8 cm long]; T free; pollen extended sulcate [unipantocolpate]; stylar canals 3 [Kingia]; storage nucellus well developed; (fruit explosively loculicidal + septifragal, vales separating periclinally and acropetally - Baxteria); n = 7; seedling?
2/2. S.W. Australia (map: from FloraBase 2004).
Synonymy: Baxteriaceae Takhtajan, Kingiaceae Schnizlein
Chemistry, Morphology, etc. Some species of Calectasia have stilt roots. Both Calectasia and Baxteria have single flowers surrounded by numerous bracts. Calectasia has a 1-locular ovary (Barrett & Dixon 2001: monograph). In Kingia the apical meristem is depressed, as in Arecaceae, and the plant is also monopodial; adventitious roots grow down to the ground in persistent sheathing leaf bases.
Additional information is taken from Chanda and Ghosh (1976: pollen), Rudall (1994: embryology), Clifford et al. (1998b: general), and Rudall and Conran (2012: floral morphology).
Phylogeny. See Rudall and Chase (1996) for the dismemberment of the old Xanthorrhoeaceae and the relationships of the genera of Dasypogonaceae.
Previous Relationships. Dasypogonaceae have often been linked with other similar-appearing xeromorphic monocots from Australia such as Xanthorrhoeaceae and Lomandraceae, as in Takhtajan (1997); for the two, see Asparagales as Xanthorhoeaceae-Xanthorhoeoideae and Asparagaceae-Lomandroideae.
Classification. The name Dasypogonales Doweld is available for this clade if needed, but if Dasypogonaceae are sister to Arecaceae, Arecales can be expanded to include both families.
ARECALES Bromhead Main Tree.
Growth monopodial, plant unbranched, stem well-developed, woody; vessels also in stem and leaf; cuticular waxes as aggregated rodlets, stomata tetracytic; leaves spiral, massive, with petiole and blade, blade developing from the upper part of the leaf, vernation reduplicate-plicate, pinnately pseudocompound, sheath closed; flowers ± sessile; ovule apotropous, ± sessile, attachment broad; seeds large [>1 cm long].
1 family, 183 genera, 2361 species.
Synonymy: Cocosales Nakai
ARECACEAE Berchtold & J. Presl, nom. cons.//Palmae Jussieu, nom. cons. et nom. alt. Back to Arecales
Flavonoid sulphates abundant; roots lacking real elongation zone, with radially elongated air spaces; sieve tubes with simple sieve plates; endodermal cells with O-shaped thickenings; cellulose fibrils in the outer epidermal walls randomly oriented; SiO2 bodies spherical, often spiny-verrucate, also associated with fibre bundles; leaf epidermal cells rectangular, hypodermal cells rectangular, longitudinally elongate; stomatal subsidiary cells with oblique cell divisions; fibre strands +, both free in mesophyll and attached to epidermes, sheaths of transverse veins fibrous, centrifugal differentiation of fibrous phloem cap of fibrovascular bundle; plant monoecious; inflorescence axillary, with basal bicarinate prophyll, inflorescence units cymose, prophylls lateral [units are cincinni]; staminate flowers: A (many, but basically trimerous), basifixed; pistillode ± +; carpellate flowers: staminode +; G 1-4 [2-10], carpels initially free; outer integument (4-)6+ cells across, inner integument 2-3(-6 - Ceroxylon) cells across, parietal tissue (0)1-5(-6) cells across, (postament +), suprachalazal area ± massive; micropylar embryo sac haustorium +; seeds 1(-10)/fruit, rounded; testa usually with two outer layers thickened, (basal portion vascularized); micropylar endosperm haustorium +, endosperm with hemicellulose [mannans], thick-walled; cotyledon not photosynthetic, collar short (with roots), primary root strong, branched.
183[list]/2361 - five groups below. Humid tropics and subtropics (warm temperate), Africa is relatively depauperate. [Photo - Flowers, Fruits.]
Age. Divergence within crown-group Arecaceae is estimated to have begun ca 110 m.y.a. (Janssen & Bremer 2004) or (78-)73, 63(-58) m.y. (Wikström et al. 2001). Bell et al. (2010) suggest the remarkably young - and surely incorrect - age of (38-)33, 31(-21) m.y. for the crown group.
Fossil Arecaceae date to ca 93 m.y. (Pan et al. 2006; Harley 2006).
1. Calamoideae Beilschmied
Plant spiny; sustained primary growth slight-0; root periderm 0; 1 (2) vessels/fibrovascular bundle; epidermal cells rectangular, anticlinal walls sinuous; adaxial subepidermal fibre bundles +; parenchyma cells near protoxylem inflated (not), longitudinal veins bridging to adaxial epidermis via vertically-elongated sclereids, lateral veins adaxial to longitudinal veins, adaxial non-vascular fibres subepidermal; internodes usu. well-developed; flowers in dyads; C valvate, basally connate; ovule basically apotropous, but funicle twisted; fruit covered by reflexed scales.
21/615. Tropical, but esp. Sri Lanka to West Samoa and Fiji.
1a. Eugeissoneae W. J. Barker & J. Dransfield
Growth sympodial, [plant hapaxanthic]; endodermal cell walls barely thickened; SiO2 bodies minute, disciform; inflorescence terminal, inflorescence units surrounded by cupule of 7-11 overlapping bracts; diad with staminate and perfect flowers; flowers large [to 7 cm long]; K connate, C woody; stamens 20-70, development centrifugal; scales small; mesocarp forming lignified stony layer, ridged, endocarp massive, becoming crushed; seeds longitudinally ruminate; n = ?
1/6. S. Thailand to Borneo (Map: from Dransfield et al. 2008b).
1b. The Rest.
Plant often lianes, climbing by ± recurved spiny structures; (leaves palmate); (inflorescence axes adnate to the internode above, or to sheath of the leaf of the next node); breeding system various; (C free); A <12; (pollen equatorially disulcate - Calameae); (style branched); fruit dry, pericarp not woody, (berry), scales large, endocarp thin; seeds 1-3, sarcotesta +, usually thick, (testa thin, dry); n = 13, 14.
20/600: Calamus (375), Daemonorops (100). Tropical, but esp. Sri Lanka to West Samoa and Fiji (map: from Uhl & Dransfield 1987).
Age. the age of this node is some 48-40 m.y. (Wikström et al. 2001).
Synonymy: Calamaceae Perleb, Lepidocaryaceae Martius, Sagaceae Schultz-Schultzenstein
[Nypoideae [Coryphoideae, Ceroxyloideae, Arecoideae]]: sustained primary growth +; root periderm +; 2 (1, 3, 4) vessels/fibrovascular bundle; anticlinal epidermal walls ± straight, adaxial subepidermal fibre bundles 0.
Age. This node is estimated to be 71-14 m.y.o. by Mennes et al. (2013).
2. Nypoideae Griffith
Growth sympodial, stem dichotomously branched; endodermal cell walls barely thickened; no centrifugal differentiation of fibrous phloem cap of fibrovascular bundle; epidermis with hydathodes, epidermal cells hexagonal to spindle-shaped, guard cells with several ledges [in t.s.], SiO2 bodies small, hat-shaped; hypodermal cells several layered, lignified, hexagonal, transversely elongate, veins bridging to epidermis via vertically-elongated sclereids, sheaths of transverse veins sclereidal, veins sinuous, irregular; inflorescence axis adnate to the internode above, racemose, staminate inflorescence a spike, carpellate inflorescence a head; P free, ± undifferentiated; staminate flowers: A 3, opposite outer P, connate, "stalk" solid, anthers extrorse; pollen with encircling sulcus; pistillode 0; carpellate flowers: staminodes 0; G 3 (4), margins conduplicate, placentation laminar to submarginal; ovule [position?], outer integument ca 10 cells across; n = ?17.
1/1: Nypa fruticans. Bengal to Queensland (map: current distribution in red, from Uhl & Dransfield 1987; Spalding et al. 2010; fossil records from places outside this area in blue, from Plaziat et al. 2001).
Synonymy: Nypaceae Le Maout & Decaisne
[Coryphoideae [Ceroxyloideae + Arecoideae]]: sieve tube with compound sieve plates; endodermal cell walls with U-shaped thickenings (thickened all around); (leaf veins bridging to epidermis by fibres); (A numerous, development centripetal); microsporogenesis simultaneous; ovule position and type various, (postament +).
Age. The age of this node may be 68-61 m.y. (Wikström et al. 2001); estimates are (98-)51(-15) m.y. in Merckx et al. (2008a).
3. Coryphoideae Burnett
(Stem branched - e.g. Caryota); septate fibres +; no centrifugal differentiation of fibrous phloem cap of fibrovascular bundle; no fibre bundles free in mesophyll, longitudinal veins with ad/abaxially elongated bridging sclereids, transverse veins with broad sheath of fibres, adaxial vein rib with 5 or more independent vascular bundles; leaves palmate or costapalmate (pinnate), (induplicate - Phoeniceae); inflorescence various, (terminal; adnate to the internode above; plant monoecious - Caryotinae), flowers solitary or in cincinni (triads); C often valvate, connate (free); microsporocyte with callose ring [not Caryota, Bismarckia]; G (1), free or postgenitally connate by style, style 0 [Caryoteae], or +, with 3 [Coryphinae] or 1 [Sabalinae] stylar canals.
45/ca 500: Coccothrinax (50). Pantropical (to warm temperate), fewer in South America, quite frequently outside tropical rain forest (map: from Uhl & Dransfield 1987).
Synonymy: Borassaceae Schultz-Schultzenstein, Coryphaceae Schultz-Schultzenstein, Phoenicaceae Burnett, Sabalaceae Schultz-Schultzenstein
[Ceroxyloideae + Arecoideae]: petiole bundles arranged in one or more Vs (scattered); sheaths of transverse veins sclereidal, veins sinuous, irregular, epidermal cells hexagonal to spindle-shaped.
4. Ceroxyloideae Drude
Plant dioecious, or flowers perfect; inflorescence racemose, spicate; (K and C elongate), (free); (A not trimerous, with trunk bundles, development centrifugal - Phytelepheae), (development centripetal - Ceroxylon); G [3-10], receptacle elongated; (seeds more than 3).
8/42. Mostly Central and W. South America, also N.E. Australia, Madagascar, Florida and the Antilles (map: from Uhl & Dransfield 1987).
Synonymy: Phytelephaceae Perleb
5. Arecoideae Beilschmied
(Stem with crownshaft [formed by elongated leaf sheaths]); (SiO2 bodies hat-shaped); hypodermal cells hexagonal, transversely elongate; (plant dioecious); flowers in triads [central (upper) flower carpellate, lateral flowers staminate] or in two vertical rows [acervuli], (inflorescences spicate); (C valvate); (A 3); (1 G fertile), style branches separate (style single, short or long); (inner integument ca 7 cells across - Cocos); n = 16.
112/1100: Bactris (240), Dypsis (165), Pinanga (120), Chamaedorea (110), Geonoma (70), Desmoncus (65<), Areca (60), Astrocaryum (50). Pantropical, the most diverse subfamily in South America (map: from Uhl & Dransfield 1987).
Synonymy: Acristaceae O. F. Cook, Ceroxylaceae Vines, Chamaedoraceae O. F. Cook, Cocosaceae Schultz-Schultzenstein, Geonomataceae O. F. Cook, Iriarteaceae O. F. Cook & Doyle, Malortieaceae O. F. Cook, Manicariaceae O. F. Cook, Moreniaceae O. F. Cook, Pseudophoenicaceae O. F. Cook, Synechanthaceae O. F. Cook
Evolution. Divergence & Distribution. Palm pollen was abundant in tropical Gondwanan areas during the later Cretaceous (Nichols & Johnson 2008). Palm leaves, pollen and/or wood are quite common and widely distributed in the later Cretaceous when global temperatures were warmer (Burnham & Johnson 2004), including in Africa and India where palms are not very diverse today. Palm pollen is even recorded from palaeo 85o N sediments dated to 53.5 m.y. in the Eocene on the Lomonosov Ridge (Sluijs et al. 2009) and from palaeo 70o S sediments dated to ca 51.9 m.y. in the Eocene off Wilkes Land in the Antarctic (Pross et al. 2012). However, by the Oligocene extra-tropical climates in general were becoming more seasonal, and so less favourable for palms away from lower latitudes.
It is suggested that Arecaceae have diversified at a constant rate since their origination in the Cretaceous ca 100 m.y. or more ago (perhaps in Laurasia) until ca 24 m.y.a., the K/T boundary passing unmarked (Couvreur et al. 2011b, esp. c). Palms then serve as markers for tropical rainforest - or perhaps a tropical rain forest-like biome (Couvreur et al. 2011b). This being said, the early evolution of the rain forest biome is still not well understood. Coiffard and Gomez (2009) even suggest that early palms may have been swamp dwellers like living basal Arecaceae (they list Calamus, Nypa, and Mauritia). Fossils (leaf, stem, fruit) from rocks in Texas of Cretaceous-Campanian age some 77 m.y. old have been identified as the modern genus Sabal; young dinosaurs might have eaten their fruits (Manchester et al. 2010a).
The past and present distributions of palms can be difficult to reconcile. Lodoicea is currently restricted to the Seychelles, although its fruits are widely distributed by the sea; ocean crust separating India and the Seychelles dates to ca 63.4 m.y. (Collier et al. 2008), so either Lodoicea is that old, or it has somehow moved onto these islands. Nypa seems to have had a more or less world-wide distribution in the early Tertiary, fossils being known from Tasmania, England (the London Clay flora), both Americas, etc. (Plaziat et al. 2001: see map above). Pollen of some species of the West Malesian Eugeissona is distinctive, being thick-walled and extended monosulcate; such pollen has been found throughout the tropics (Dransfield et al. 2008b: records need checking). Wood of Coryphoideae-Crysophileae, a New World group, has been found in Lower Oligocene to Upper Miocene deposits in France (Thomas & de Franceschi 2012). Finally, calamoid palm leaves and fruits are found in Late Eocene rocks on the very southern part of New Zealand (Hartwich et al. 2010); the closest Calamoideae grow in eastern Australia, a rather less dramatic range difference than for Nypa, but still noteworthy.
Despite the size of many palms and of their fruits, dispersal rather than vicariance is increasingly frequently being invoked to explain many apects of the present distribution of the family (Bacon et al. 2012a, b; Baker & Couvreur 2012). The scattered and apparently ancient Gondwanan distribution of Ceroxyloideae is probably best explained by several mid-Tertiary trans-oceanic dispersal events (Trénel et al. 2007). Species of Hyophorbe (Arecoideae-Chamaedoreeae) are disjunct on the Mascarenes, and the genus may have radiated in that area on islands that are now submerged, hopping from island to island (Cuenca et al. 2007); some Myrtaceae, Begoniaceae, and Sapotaceae may also be island-hoppers.
Palms are poorly represented on mainland Africa, but they are richer in Madagascar (Snow 1981); the radiation of Dypsis and the other Dypsidinae (Arecoideae-Areceae) there - some 165 species - is particularly spectacular; Madagascan palms lack spines, etc, unlike their African relatives, perhepas because of the absence of large herbivores on the island (Dransfield & Rakotoarinivo 2011). In Africa palms became less common at the beginning of the Tertiary and again at the end of the Eocene ca 34 m.y.a. (Pan et al. 2006; Harley 2006: summary of the fossil record; Kissling et al 2012a); overall, the paucity of palms on the continent can perhaps be explained by the increase in diversification rates elsewhere (Bacon et al. 2012b) and also because palm diversity there is the historical legacy of past climatic events (since the Late Miocene ca 10 m.y.a.) that is evident in present distributions (Blanch-Overgaard et al. 2013).
The diversity and diversification of palms in the New World and the Indo-Malayan areas has been linked to the persistence of the relatively warm and wet areas that they favour, and also the environmental heterogeneity of those areas (Svenning et al. 2008; Kissling et al. 2012b; Bacon et al. 2012b). Arecoideae-Bactridineae diverged in America at the end of the Eocene (Eiserhardt et al. 2011a); for details of diversification of palms worldwide, see Kissling et al. (2012a, b), Bacon et al. (2012a, b), Baker and Couvreur (2012), etc., while Bjorholm et al. (2006) discussed patterns of diversity in neotropical subfamilies, the Antilles excluded. Roncal et al. (2008) explored the biogeography of Antillean palms and Roncal et al. (2010) examined the biogeography of the mostly understory Geonomateae. Here crown group divergence began in the Oligocene and species are older than Quaternary refugium theory would predict; again, there seems to have been considerable dispersal. In the Old World, Couvreur et al. (2011b) suggested that the stem age of the Malesia-centred Calamus, with some 400 or more species, is only 24 m. years. For diversification in S.E. Asian/Malesian palms, see Baker and Couvreur (2012) and Bacon et al. (2013).
Nadot et al. (2011) mapped androecial evolution on a phylogenetic tree; developmental details of polyandrous flowers vary considerably, but apart from Phytelepheae (Uhl & Moore 1977a), the androecium is basically trimerous, the stamens are supplied by separate bundles, and in a few genera (Socratea, Wettinia) there are antesepalous stamen pairs (see also Alapetite et al 2014: Ptychospermatinae; Uhl 1976 and Uhl & Moore 1980: androecial development). Carpels in all palms studied are initially free (Dransfield et al. 2008b), and perhaps connected with this, apocarpy has probably evolved some four times within Arecaceae (Rudall et al. 2011b). Loo et al. (2006) thought that the evolution of protogyny in Arecinae might be correlated with with a radiation in Pinanga and diversification in pollen morphology and genome size.
Ecology & Physiology. Palm fossils are used as climatic markers by palaeontologists (e.g. Greenwood & Wing 1995; Sluijs et al. 2009) based on the climatic restrictions of present-day palms. Palms are very susceptible to frost, most having only a single vegetative meristem and being unable to produce replacement meristems if the first is killed. They are usually found in places where the mean annual temperature is more than 10° C, mean temperatures in the coldest month are more than 5°, and the coldest temperature does not dip below -10° C (Larcher & Winter 1981; Greenwood & Wing 1995; Tomlinson 2006; Couvreur et al. 2011c; Kissling et al. 2012b).
In their analysis of major functional traits in vascular plants, Cornwell et al. (2014) noted that Arecaceae were both relatively large and had relatively large seeds compared with other monocots, and this was associated with a strong preference for humid and warm conditions. Eiserhardt et al. (2011b) think about the distribution of palms world-wide in the context of ecological determinants both of geography and diversity. The suspects are very much as one might expect, with climatic limitations (see above) having a major effect on broad-scale patterns while dispersal affects patterns at all scales. Interestingly, over two thirds of the palm genera that grow outside tropical rainforest are members of Coryphoideae (Thomas & de Franceschi 2012).
Arecaceae include many examples of the eco-morphological combination of shaded conditions, net-veined leaves and fleshy fruits that has evolved several times in monocots (Givnish et al. 2005, 2006b). In America genera like are particularly common in the understory.
Palms may be very conspicuous components of the vegetation. Nypa dominates some mangrove habitats, preferring less saline conditions than many other mangrove plants; it is found along rivers up to the limit of tidal influences (for the evolution of the mangrove habitat, see Rhizophoraceae; see also Clade Asymmetries). Chomicki et al. (2014a) discussed how air reaches the submerged roots; they found that lenticellar tissue develops on the leaf base after the frond rhachis falls away, and air then moves down canals into the roots. Calamoid palms are a very important liane group in the South East Asian forests (Gentry 1991). Arecaceae are disproportionally well represented among the common trees with 10 cm or more d.b.h. in Amazonian forests, although they are not notably numerous in terms of species (ter Steege et al. 2103). They can attain very high population densities compared with the other common species (ter Steege et al. 2013), although of course most palms are single-stemmed plants.
Arecaceae are the largest clade of woody monocots (bamboos are the other large woody clade). They have the oldest functioning xylem elements and sieve tubes in vascular plants, but how the conducting system remains functional is unknown. Since the oldest palm is hundreds of years old and it is commonly thought that there is no secondary thickening, the vascular tissue at the base of the stem must remain active for the whole life of the plant; ophysiologically and metabolically functional cells can be very old (Tomlinson & Huggett 2012). However, old palm stems are not inert. Renninger and Phillips (2012, 2013; c.f. Tomlinson & Quinn 2013) found that the stems of Iriartea, at least, lengthened appreciably over time, and this was accompanied by a straightening of the spiral course of the vascular bundles; lengthening has also been noticed in other palms (Waterhouse & Quinn 1978). The walls of vascular fibres continue to thicken, so increasing stem stiffness as the tree grows bigger (Tomlinson et al. 2011). Ground tissues in both stem and root may remain undifferentiated for some time, with limited mitosis and/or cell expansion and/or formation of schizogenous lacunae and the trunk markedly thickening and lengthening (diffuse secondary thickening - Tomlinson 1961c; sustained primary growth Waterhouse & Quinn 1978; see also Tomlinson et al. 2009, 2011). This ability of cells to remain metabolically active may help explain the functional longevity of palm vascular tissue. There are also persistent reports that at least some palms have monocot-type secondary thickening (Angyalossy et al. 2008; Botánico & Angyalossy 2013). Waterhouse and Quinn (1978) suggested that in some palms there was initially sustained primary growth and this was followed by growth in which the trunk did not increase in width and was strictly columnar. Even in primary growth there is considerable variation within the family, differentiation of vascular tissue in Calamus being particularly distinctive (Tomlinson & Spangler 2002). The longevity of cells in seed plant vascular tissue in general would repay investigation - some xylem parenchyma cells even in broad-leaved angiosperms may remain metabolically active for 200 years or so (Spicer & Holbrook 2007), xylem in lianas perhaps being particularly long-lived (refs in Angyalossy et al. 2012).
Vessels in Rhapis excelsa are quite resistant to embolism, but what goes on in the very long vessels of some calamoid palms - some over 0.5 mm wide and to almost 4 m long, and spanning (8-)13(-18) internodes - is unclear (Sperry 1986; Fisher et al. 2002; Tomlinson 2006b) and so apparently making them susceptible to cavitation; Tomlinson (2006b) thought of xylem function in the context of stem length. Davis (1961) noted that root pressures in several palms he studied in India were very high, sometimes exceeding the height of the plant, and this could help remove cavitations (see also Cao et al. 2012).
Pollination Biology & Seed Dispersal. Pollination is predominantly by insects, whether beetles (mainly Nitidulae and Cuculionidae-Derelomini [weevils]), bees, especially Halictidae (sweat bees) and Meliponini (stingless bees), and flies, which may visit especially understory palms (Henderson 1986, 2002; Silberbauer-Gottsberger 1990; Barfod et al. 2011). However, there is no clear correlation of pollen morphology with pollinator (Sannier et al. 2009). There may be mimicry of staminate by carpellate flowers in Geonoma (Stauffer et al. 2002 and references); presentation of the nectar of both flower types in a similar fashion (c.f. Meliaceae) may be a related explanation. Volatiles produced by the leaves of Chamaerops humilis attract its weevil pollinator (Dufaÿ et al. 2003), while thermogenesis has been detected in the flowers of some Arecaceae, mostly in flowers lacking nectar (Silberbauer-Gottsberger 1990; Seymour 2001). Beetles may lay eggs in staminate inflorescences (Silberbauer-Gottsberger 1990). The speciose New World Chamaedoreeae (Arecoideae) all have raphides in the flowers and in Chamaedorea these are particularly common in the perianth and gynoecium; there are other potentially protective structures in the flowers (Askgaard et al. 2008).
Seed size increased considerably in stem Arecaceae (Moles et al. 2005a; Linkies et al. 2010: Sims 2012; Cornwell et al. 2014). This may be associated with their woody habit, but seeds of Arecaceae are absolutely large when compared with those of all other angiosperms. Their dispersal is primarily by animals, although Cocos nucifera, dispersed by sea currents, is a notable exception (Zona & Henderson 1989; Henderson 2002).
Vegetative Variation. Seedling morphology is very variable within Arecaceae (Henderson 2002, 2006; Tillich 2007). Seedlings of palms with aerial stems usually undergo a period - up to 50 years - of establishment growth (Henderson 2002 and references). During this time the apical meristem becomes gradually larger, as does the width of the axis it produces, and only when it has reached adult size does elongation growth of the trunk occur (but see above). With some exceptions, the size of the apical meristem and hence the width of the trunk remains constant for rest of the life of the palm. Iriarteeae (Arecoideae) are one of those exceptions. Here there is no underground establishment growth, and the trunk becomes gradually wider as it grows, being narrowly obconical overall. A plant with such a stem is obviously highly unstable, but massive prop roots develop from the lower part of the trunk and stabilise it. The base of the stem rots away, and the older plant then depends entirely on its prop roots for support, water, etc..
Despite appearances, the leaves of all palms are simple. The deep lobes in simple palm leaves and the leaflets in apparently compound leaves, are commonly thought of as being the result of cell death. However, a detailed study of species of Chamaedorea showed that the process is more like abscission (Nowak et al. 2007, 2008), although nothing (apart, sometimes, from the lamina margin, see below) falls off. The parts that will separate first become thin, then split; tissue at the zone of separation becomes lignified, suberised, or covered by a cuticle, so protecting the rest of the blade. Details of the timing of this process may differ even between closely-related species (Nowak et al. 2007, 2008). The leaf blade early becomes stongly plicate, and blade separation occurs in various places with respect to these plications (see also Kaplan et al. 1982: good review of the earlier literature; Gunawardena & Dengler 2006). In a number of palms thin "reins" hang down from the sides of the leaves; these are the lamina margins of the originally simple blade. Fibrous filaments occuring between the leaflets is other evidence for the originally simple nature of the leaf. Given the distinctive nature of compound palm leaves, it is not surprising to find that KNOX genes are not involved in their development, although they are in the compound leaves of broad-leaved angiosperms (Nowak et al. 2011). However, the blade of a palm leaf may develop from the upper part of the leaf, as in broad-leaved angiosperms (Gunawardena & Dengler 2006).
Fibers at the bases of the leaves are produced by the decay of the sheaths, while the spines found on so many palms are produced in various ways. They may be modified leaflets (Phoenix), adventitious roots (Crysophila, but relatively uncommon), partly detaching outer parts of the stem that become erect, etc. (Tomlinson 1962b; Tomlinson et al. 2011).
Many Calamoideae (the rattans) and some Arecoideae (Desmoncos), are climbers, either by the aid of a long, hook-bearing apical portion of the leaf, the cirrus, and also, in Calamus and relatives by a very much modified long and very thin inflorescence axis with recurved spines, the flagellum, that is adnate to the sheath of the leaf of the node immediately above. These climbing aids are remarkably effective, indeed, Calamus is sometimes called the lawyer vine, because once you are caught by the the flagellum, it can be very difficult to get free. However, they eventually fall off with the leaves, and the stems, which can reach lengths of up to some 200 m, then tend to sag (Isnard & Rowe 2008 for details).
Dichotomous branching is scattered in the family, having first been recorded from Hyphaene thebaica by Schoute in 1909 (Fisher 1974 and references).
Plant-Animal Interactions. Satyrinae-Morphini butterfly larvae may be found on Arecaceae, along with larvae of Hispinae-Cassidinae beetles; these latter can be serious pests of oil palms and other commercial or ornamental palms (Chaboo 2007). The move of satyrines on to palms was important in the diversification of the former (Peña et al. 2011; Nylin et al. 2014). Stem Bruchinae - the highly speciose seed beetles, now found mostly on Fabaceae - are about 85-82.6 m.y. old (age spread far greater); that is, they evolved long before Fabaceae, and their original diet may have been seeds of Arecaceae (Kergoat et al. 2005b, 2011). A male of the (now) palm-eating Pachymerini was found in Canadian amber dated at ca 79 m.y. (Poinar 2005).
Genes & Genomes. The rate of molecular evolution in Arecaceae is rather low, as might be expected from a woody plant with a relatively long generation time, and is ca 0.0014 substitutions/site/m.y.; this is interpreted as a reduction in the rate of molecular evolution (Smith & Donoghue 2008; also Gaut et al. 1996: comparison between Poaceae and Arecaceae).
Economic Importance. Domestication and cultivation of the coconut, Cocos nucifera Arecoideae-Cocoseae), seems to have occurred independently in southern India and the Malesian archipelago (Gunn et al. 2011). There is much debate as to where Cocos originated. Gunn (2004) suggested that it it might be sister to the New World Parajubaea and be at least 22 m.y. old, while Meerow et al. (2009a, esp. b) found a sister relationship with the New World Syagrus from which it diverged (39.5-)34.9(-20.7) m.y.a., crown group divergence beginning ca 11 m.y.a. (Meerow et al. 2009b: 95% HPD limits). On the other hand, Kapgate (2009) found fruits in the Deccan Intertrappean Beds that he thought were like those of Cocos and that are of Late Cretaceous to Early Tertiary age (ca 65.5 m.y.: Gómez-Navarro et al. 2009 for additional references) and Gómez-Navarro et al. (2009) found fruits that they compared with Cocos from northern Colombia that are perhaps a little younger - about 58 m.y. old. Something is wrong.
Elaeis guineensis (also Cocoseae), the oil palm, is a major tropical plantation crop; its cultivation has been responsible for particularly massive deforestation.
Chemistry, Morphology, etc. Horn et al. (2008, 2009b, 2010a, esp. 2009b) and especially Tomlinson et al. (2011) look at various aspects of lamina anatomy in the context of the phylogeny of the family; this has in part been integrated above, but there is widespread homoplasy in the characters. Parthasarathy (1974) described phloem development. According to Arber (1925), the vascular bundles are not amphivasal. "Leaflets" of induplicate leaves are V-shaped in cross section, those of reduplicate leaves are inverted V-shaped (see also Kaplan 1997, vol. 2: chap. 17 for leaf morphology).
For variation in details of the inflorescence units in Arecoideae-Chamaedoreae, which have acervuli, that is, modified largely ebracteate cincinni, see Uhl and Moore (1978), Cuenca et al. (2009), and Ortega-Chávez & Stauffer 2011). The flower in general (e.g. Rudall et al. 2003b; Uhl & Moore 1971) and pollen in particular (see Harley 1999b; Harley & Baker 2001; Dransfield et al. 2008b) show a considerable amount of variation. The number of vascular traces to the sepals and petals is very variable (Uhl & Moore 1978). The stamens are never adnate to the corolla/inner tepals in staminate flowers, although in carpellate flowers of Roystonea the corolla has a broad staminal cup at the base, and in carpellate flowers of Geonomeae (Arecoideae), both the calyx and corolla are connate and the stamens are adnate to the latter (Stauffer & Endress 2003), and the style there is more or less gynobasic. Microsporogenesis is simultaneous in some Coryphoideae and Arecoideae (Harley 1999a; Sannier et al. 2006). Variaton in gynoecial development is especially pronounced in Coryphoideae, where there are all intermediates between syncarpous and apocarpous gynoecia, and sometimes only a single carpel. Cocos may have a bisporic 8-nucleate embryo sac and ovules that lack parietal tissue (Robertson 1976). For details on the development of the pericarp, see Bobrov et al. (2012a, b); Dransfield et al. (2008b) note that the stony layer of Eugeissona differs from that of other Arecaceae. In Voaniola n = 298 or more.
Students of palms are fortunate in having a series of major works devoted to the family; these include von Martius's (and his collaborators) magnificent Historia naturalis palmarum (1823-1850 - see also Martius 2010), surely one of the greatest of all botanical publications, Corner (1966), Uhl and Dransfield (1987), Tomlinson (1990), Henderson (2002), Dransfield et al. (2005, 2008b) and Tomlinson et al. (2011).
Additional information may be found in Moore (1973), Zona (1997: esp. south east U.S.A.), Dransfield and Uhl (1998), and Tomlinson (2006a), all general, Uhl (1972: Nypa), Tomlinson (1970: vascular organization in the stem), Tomlinson (1974: stomatal development), Seubert (1998 and references: root anatomy), Thomas and di Franceschi (2013: stem anatomy), Gunawardena and Dengler (2006: leaf development), Prychid et al. (2004) and Piperno (2006), both SiO2 bodies/phytoliths, Uhl and Dranfield (1984) and Balhara et al. (2013: Ceroxylon), both floral development, Stauffer et al. (2009: labyrinthine nectaries), Harley and Dransfield (2003: triporate pollen), Sannier et al. (2007: microsporogenesis evolution, Ceroxyloideae not included), Uhl and Moore (1971: gynoecium), Zona (2004: embryo raphides), Henderson (2006: detailed descriptions of germination, not integrated with phylogeny), Essig (2008) and Romanov et al. (2011), both fruit anatomy.
Phylogeny. [[Nypoideae + Calamoideae] (strong support for that clade) + the rest of the family (moderate support)] formed a trichotomy in a three-gene study by Asmussen et al. (2000); other characters supported these general relationships. Soltis et al. (2007a) also recovered a well-supported clade [Nypoideae + Calamoideae]. However, Calamoideae were probably sister to all other Arecaceae in other studies, if some morphological groupings were not supported by molecular data (Hahn 2002a, b; see also Baker et al. 1999a; Asmussen & Chase 2001; Lewis & Doyle 2001). Henderson and Stevenson (2006), after a analysis of morphological and anatomical features for selected genera, discussed groupings, relationships and character evolution. They found that Phoenix and Thrinax appeared as successively sister to the rest of the family, which seemed even then rather unlikely. However, Asmussen et al. (2006: very good generic-level sampling, four genes) clarified this confusion and presented the rather well supported set of relationships summarized in the tree here; those parts less well supported (the monophyly of Ceroxyloideae and Arecoideae) were strongly supported by low copy number nuclear DNA data (W. J. Baker, unpubl. data, in Asmussen et al. 2006). These relationships were confirmed in the comprehensive analysis of Baker et al. (2009), although the position of Nypoideae was less well supported than that of the other subfamilies.
For morphology, phylogeny and classification in Calamoideae, see Baker et al. (1999b, 2000a, b, c); there are three main clades, and Eugeissona is probably sister to the rest. Coryphoideae include Caryoteae, previously placed in Arecoideae (Uhl and Dransfield 1987; see also Dransfield et al. 2008a for a phylogeny). A number of taxa have diversified on islands, and Bacon et al. (2012) discusssed the relationships of several genera of these that belong to Trachycarpeae. Ceroxyloideae include Phytelephantoideae (Dransfield et al. 2005). Phytelephas and its relatives have 4-merous flowers with up to 1000 centrifugal stamens (Palandra) and 10 carpels; Palandra also has monopodial flower clusters, unique in the family.
Baker et al. (2011, 2012) examined phylogenetic relationships within Arecoideae; tribes were monophyletic, but relationships within the large Areceae were unclear (see also Lewis & Doyle 2002; Baker et al. 2006). Norup et al. (2006) discuss generic limits in Areceae; a distinctive crown shaft is a tribal apomorphy. Loo et al. (2006) examined relationships in Arecinae (betel nut and relatives). Gunn (2004) provided a phylogeny of Cocoseae as did Noblick et al. (2013: morphological analysis); the latter found a paraphyletic Syagrus that included Cocos, but bootstrap values were nearly all below 50%. Eiserhardt et al. (2011a) discussed phylogenteic relationships in the spiny Neotropical Bactridinae, which includes the climbing Desmoncus. Cuenca and Asmussen-Lange (2007) and Cuenca et al. (2007, 2008) discuss the phylogeny and biogeography of the largely New World understory Chamaedoreeae; for the phylogeny of Chamaedorea itself, see Thomas et al. (2006). For relationships within the East Malesian to Pacific Ptychospermatinae and integration with variation in stamen number, see Alapetite et al. (2014).
Classification. Dransfield et al. (2008b, see also Dransfield et al. 2005) present the classification followed above. Arecoideae above are the Arecoideae of Uhl and Dransfield (1987), but minus Caryoteae, and they also include Ceroxyloideae (Hahn 2002b; also Baker et al. 1999a), basically, the arecoid line of Moore (1973: see Dransfield et al. 2005). Govaerts and Dransfield (2005) provide a checklist for the family, for which, see also the World Checklist of Monocots, but the best - and ever improving - resource for the family is PALMweb.
Previous relationships. The old Spadiciflorae included those taxa with a spadix and often also a spathe. Families included, Pandanaceae, Cyclanthaceae, Araceae and Arecaceae, are now placed in three immediately unrelated orders, Pandanales, Alismatales and Arecales. Engler (1892) linked Pandanaceae, Arecaceae and Cyclanthaceae.
Botanical Trivia. Arecaceae have the largest leaf - Raphia sp., ca 25 x 3 m; the largest inflorescence - Corypha umbraculifera, ca 7.5 m long with some 10,000,000 flowers and 5280 m of flower-bearing axes (Tomlinson & Soderholm 1975); the largest seed - Lodoicea maldavica, to 50 cm long and 15-30 kg, which in turn produces the longest cotyledon (strictly speaking, an apocole or elongated, unifacial, non-photosynthetic part of the cotyledonary hyperphyll) which may be "several yards" or "twelve feet or more" long (Thiselton-Dyer 1910); the longest unbranched stems, perhaps up to 200 m long in Calamus manan; xylem elements and sieve tubes can remain functional hundreds of years old (for possible secondary thickening, see above); and perhaps the longest vessels, to 3.96 m long in some calamoid palms (Tomlinson & Spangler 2002). They also have close to the oldest viable seeds; a seed of Phoenix dactylifera perhaps 2,000 years old has recently been germinated (Sallon et al. 2008; see also Kew Magazine, Winter 2008: 28-31).