EMBRYOPSIDA Pirani & Prado
Gametophyte dominant, independent, multicellular, not motile, initially ±globular; showing gravitropism; acquisition of phenylalanine lysase [PAL], microbial terpene synthase-like genes +, triterpenoids produced by CYP716 enzymes, phenylpropanoid metabolism [development of phenolic network], xyloglucans in primary cell wall, side chains charged; plant poikilohydrous [protoplasm dessication tolerant], ectohydrous [free water outside plant physiologically important]; thalloid, leafy, with single-celled apical meristem, tissues little differentiated, rhizoids +, unicellular; chloroplasts several per cell, pyrenoids 0; glycolate metabolism in leaf peroxisomes [glyoxysomes]; centrioles/centrosomes in vegetative cells 0, microtubules with γ-tubulin along their lengths [?here], interphase microtubules form hoop-like system; metaphase spindle anastral, predictive preprophase band + [with microtubules and F-actin; where new cell wall will form], phragmoplast + [cell wall deposition centrifugal, from around the anaphase spindle], plasmodesmata +; antheridia and archegonia jacketed, surficial; blepharoplast +, centrioles develop de novo, bicentriole pair coaxial, separate at midpoint, centrioles rotate, associated with basal bodies of cilia, multilayered structure + [4 layers: L1, L4, tubules; L2, L3, short vertical lamellae] (0), spline + [tubules from L1 encircling spermatid], basal body 200-250 nm long, associated with amorphous electron-dense material, microtubules in basal end lacking symmetry, stellate array of filaments in transition zone extended, axonemal cap 0 [microtubules disorganized at apex of cilium]; male gametes [spermatozoids] with a left-handed coil, cilia 2, lateral; oogamy; sporophyte multicellular, cuticle +, plane of first cell division transverse [with respect to long axis of archegonium/embryo sac], sporangium and upper part of seta developing from epibasal cell [towards the archegonial neck, exoscopic], with at least transient apical cell [?level], initially surrounded by and dependent on gametophyte, placental transfer cells +, in both sporophyte and gametophyte, wall ingrowths develop early; suspensor/foot +, cells at foot tip somewhat haustorial; sporangium +, single, terminal, dehiscence longitudinal; meiosis sporic, monoplastidic, MTOC [MTOC = microtubule organizing centre] associated with plastid, sporocytes 4-lobed, cytokinesis simultaneous, preceding nuclear division, quadripolar microtubule system +; wall development both centripetal and centrifugal, 1000 spores/sporangium, sporopollenin in the spore wall laid down in association with trilamellar layers [white-line centred lamellae; tripartite lamellae]; nuclear genome size [1C] <1.4 pg, main telomere sequence motif TTTAGGG, LEAFY and KNOX1 and KNOX2 genes present, ethylene involved in cell elongation; chloroplast genome with close association between trnLUAA and trnFGAA genes [precursors for starch synthesis], tufA gene moved to nucleus; mitochondrial trnS(gcu) and trnN(guu) genes +.
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 immediate common ancestor of the group,  contains explanatory material, () features common in clade, exact status unclear.
Abscisic acid, L- and D-methionine distinguished metabolically; pro- and metaphase spindles acentric; class 1 KNOX genes expressed in sporangium alone; sporangium wall 4≤ cells across [≡ eusporangium], tapetum +, secreting sporopollenin, which obscures outer white-line centred lamellae, columella +, developing from endothecial cells; stomata +, on sporangium, anomocytic, cell lineage that produces them with symmetric divisions [perigenous]; underlying similarities in the development of conducting tissue and of rhizoids/root hairs; spores trilete; shoot meristem patterning gene families expressed; MIKC, MI*K*C* genes, post-transcriptional editing of chloroplast genes; gain of three group II mitochondrial introns, mitochondrial trnS(gcu) and trnN(guu) genes 0.
[Anthocerophyta + Polysporangiophyta]: gametophyte leafless; archegonia embedded/sunken [only neck protruding]; sporophyte long-lived, chlorophyllous; cell walls with xylans.
Sporophyte well developed, branched, branching apical, dichotomous, potentially indeterminate; hydroids +; stomata on stem; sporangia several, terminal; spore walls not multilamellate [?here].
Vascular tissue + [tracheids, walls with bars of secondary thickening]; stomata involved in gas exchange.
EXTANT TRACHEOPHYTA / VASCULAR PLANTS
Sporophyte with photosynthetic red light response, stomata open in response to blue light; plant homoiohydrous [water content of protoplasm relatively stable]; control of leaf hydration passive; plant endohydrous [physiologically important free water inside plant]; sporophyte with polar auxin transport, PIN [auxin efflux facilitator] involved; (condensed or nonhydrolyzable tannins/proanthocyanidins +); xyloglucans with side chains uncharged [?level], in secondary walls of vascular and mechanical tissue; lignins +; roots +, root hairs and root cap +; stem apex multicellular, with cytohistochemical zonation, plasmodesmata formation based on cell lineage; vascular development acropetal, tracheids +, in both protoxylem and metaxylem, G- and S-types; sieve cells + [nucleus degenerating]; endodermis +; leaves/sporophylls spirally arranged, blades with mean venation density ca 1.8 mm/mm2 [to 5 mm/mm2], all epidermal cells with chloroplasts; sporangia adaxial, columella 0; tapetum glandular; ?position of transfer cells; MTOCs not associated with plastids, basal body 350-550 nm long, stellate array in transition region initially joining microtubule triplets; suspensor +, shoot apex developing away from micropyle/archegonial neck [from hypobasal cell, endoscopic], root lateral with respect to the longitudinal axis of the embryo [plant homorhizic].[MONILOPHYTA + LIGNOPHYTA]
Sporophyte growth ± monopodial, branching spiral; roots endomycorrhizal [with Glomeromycota],lateral roots +, endogenous; G-type tracheids +, with scalariform-bordered pits; leaves with apical/marginal growth, venation development basipetal, growth determinate; sporangium dehiscence by a single longitudinal slit; cells polyplastidic, MTOCs diffuse, perinuclear, migratory; blepharoplasts +, paired, with electron-dense material, centrioles on periphery, male gametes multiciliate; chloroplast long single copy ca 30kb inversion [from psbM to ycf2]; mitochondrion with loss of 4 genes, absence of numerous group II introns; LITTLE ZIPPER proteins.
Sporophyte woody; stem branching lateral, meristems axillary; lateral root origin from the pericycle; cork cambium + [producing cork abaxially], vascular cambium bifacial [producing phloem abaxially and xylem adaxially].
Growth of plant bipolar [roots with positive geotropic response]; plants heterosporous; megasporangium surrounded by cupule [i.e. = unitegmic ovule, cupule = integument]; pollen lands on ovule; megaspore germination endosporic [female gametophyte initially retained on the plant].
EXTANT SEED PLANTS / SPERMATOPHYTA
Plant evergreen; nicotinic acid metabolised to trigonelline, (cyanogenesis via tyrosine pathway); microbial terpene synthase-like genes 0; primary cell walls rich in xyloglucans and/or glucomannans, 25-30% pectin [Type I walls]; lignin chains started by monolignol dimerization [resinols common], particularly with guaiacyl and p-hydroxyphenyl [G + H] units [sinapyl units uncommon, no Maüle reaction]; root stele diarch to pentarch, xylem and phloem originating on alternating radii, cork cambium deep seated; stem apical meristem complex [with quiescent centre, etc.], plasmodesma density in SAM 1.6-6.2[mean]/μm2 [interface-specific plasmodesmatal network]; eustele +, protoxylem endarch, endodermis 0; 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 +; cork cambium superficial; leaf nodes 1:1, a single trace leaving the vascular sympodium; leaf vascular bundles amphicribral; guard cells the only epidermal cells with chloroplasts, stomatal pore with active opening in response to leaf hydration, control by abscisic acid, metabolic regulation of water use efficiency, etc.; axillary buds +, exogenous; prophylls two, lateral; leaves with petiole and lamina, development basipetal, lamina simple; sporangia borne on sporophylls; spores not dormant; microsporophylls aggregated in indeterminate cones/strobili; grains monosulcate, aperture in ana- position [distal], primexine + [involved in exine pattern formation with deposition of sporopollenin from tapetum there], exine and intine homogeneous, exine alveolar/honeycomb; ovules with parietal tissue [= crassinucellate], megaspore tetrad linear, functional megaspore single, chalazal, sporopollenin 0; gametophyte ± wholly dependent on sporophyte, development initially endosporic [apical cell 0, rhizoids 0, etc.]; male gametophyte with tube developing from distal end of grain, male gametes two, developing after pollination, with cell walls; female gametophyte initially syncytial, walls then surrounding individual nuclei; embryo cellular ab initio, suspensor short-minute, embryonic axis straight [shoot and root at opposite ends; plant allorhizic], cotyledons 2; embryo ± dormant; chloroplast ycf2 gene in inverted repeat, trans splicing of five mitochondrial group II introns, rpl6 gene absent; whole nuclear genome duplication [ζ - zeta - duplication], two copies of LEAFY gene, PHY gene duplications [three - [BP [A/N + C/O]] - copies], 5.8S and 5S rDNA in separate clusters.
ANGIOSPERMAE / MAGNOLIOPHYTA
Lignans, O-methyl flavonols, dihydroflavonols, triterpenoid oleanane, apigenin and/or luteolin scattered, [cyanogenesis in ANA grade?], lignin also with syringyl units common [G + S lignin, positive Maüle reaction - syringyl:guaiacyl ratio more than 2-2.5:1], hemicelluloses as xyloglucans; root cap meristem closed (open); pith relatively inconspicuous, lateral roots initiated immediately to the side of [when diarch] or opposite xylem poles; origin of epidermis with no clear pattern [probably from inner layer of root cap], trichoblasts [differentiated root hair-forming cells] 0, hypodermis suberised and with Casparian strip [= exodermis]; shoot apex with tunica-corpus construction, tunica 2-layered; 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, not occluding pores of plate, companion cell and sieve tube from same mother cell; ?phloem loading/sugar transport; nodes 1:?; dark reversal Pfr → Pr; protoplasm dessication tolerant [plant poikilohydric]; stomata brachyparacytic [ends of subsidiary cells level with ends of pore], outer stomatal ledges producing vestibule, reduction in stomatal conductance with increasing CO2 concentration; lamina formed from the primordial leaf apex, margins toothed, development of venation acropetal, overall growth ± diffuse, secondary veins pinnate, fine venation hierarchical-reticulate, (1.7-)4.1(-5.7) mm/mm2, vein endings free; flowers perfect, pedicellate, ± haplomorphic, protogynous; parts free, numbers variable, development centripetal; P +, ?insertion, 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], each theca dehiscing longitudinally by a common slit, ± embedded in the filament, walls with at least outer secondary parietal cells dividing, endothecium +, cells elongated at right angles to long axis of anther; tapetal cells binucleate; microspore mother cells in a block, microsporogenesis successive, walls developing by centripetal furrowing; pollen subspherical, tectum continuous or microperforate, ektexine columellate, endexine lamellate only in the apertural regions, thin, compact, intine in apertural areas thick, pollenkitt +; nectary 0; carpels present, superior, free, several, ascidiate [postgenital occlusion by secretion], stylulus at most short [shorter than ovary], hollow, cavity not lined by distinct epidermal layer, stigma ± decurrent, carinal, dry; suprastylar extragynoecial compitum +; 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, nucellar cap?; megasporocyte single, hypodermal, functional megaspore lacking cuticle; female gametophyte lacking chlorophyll [no photosynthesis], four-celled [one module, nucleus of egg cell sister to one of the polar nuclei]; ovule not increasing in size between pollination and fertilization; pollen grains land on stigma, bicellular at dispersal, mature male gametophyte tricellular, germinating in less than 3 hours, pollen tube elongated, unbranched, growing towards the ovule, 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, ciliae 0, siphonogamy; double fertilization +, ovules aborting unless fertilized; P deciduous in fruit; mature seed much larger than fertilized ovule, small [<5 mm long], dry [no sarcotesta], exotestal; endosperm +, cellular, development heteropolar [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, embryo short [<¼ length of seed]; plastid and mitochondrial transmission maternal; Arabidopsis-type telomeres [(TTTAGGG)n]; nuclear genome size [1C] <1.4 pg [mean 1C = 18.1 pg, 1 pg = 109 base pairs], whole nuclear genome duplication [ε/epsilon event]; 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, palaeo AP3 and PI genes [paralogous B-class genes] +, with "DEAER" motif, SEP3/LOFSEP and three copies of the PHY gene, [PHYB [PHYA + PHYC]]; chloroplast chlB, -L, -N, trnP-GGG genes 0.
[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]]]]: phloem loading passive, via symplast, plasmodesmata numerous; vessel elements with scalariform perforation plates in primary xylem; essential oils in specialized cells [lamina and P ± pellucid-punctate]; tension wood + [reaction wood: with gelatinous fibres, G-fibres, on adaxial side of branch/stem junction]; anther wall with outer secondary parietal cell layer dividing; tectum reticulate; 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 [?here]; pollen tube growth intra-gynoecial; extragynoecial compitum 0; carpels plicate [?here]; 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 0, CYP716 trterpenoid enzymes 0, benzylisoquinoline alkaloids 0, hemicelluloses as xylan; root epidermis developed from outer layer of cortex; endodermal cells with U-shaped thickenings; cork cambium [uncommon] superficial; stele oligo- to polyarch, medullated [with prominent pith], lateral roots arise opposite phloem poles; stem primary thickening meristem +; vascular development bidirectional, bundles scattered, (amphivasal), vascular cambium 0 [bundles closed]; tension wood 0; vessel elements in roots 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 and forming a fimbrial vein, transverse veinlets +, unbranched [leaf blade characters: ?level], vein/veinlet endings not free, margins entire, Vorläuferspitze +, base broad, ensheathing the stem, sheath open, petiole 0; 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 [A/T primordia often associated, and/or A vascularized from T trace], anther and filament more or less sharply distinguished, anthers subbasifixed, wall with two secondary parietal cell layers, inner producing the middle layer [monocot type]; pollen reticulations coarse in the middle, finer at ends of grain, infratectal layer granular; G , with congenital intercarpellary fusion, opposite outer tepals [thus median member abaxial], placentation axile; compitum +; ovule with outer integument often largely dermal in origin, parietal tissue 1 cell across; antipodal cells persistent, proliferating; fruit a loculicidal capsule; seed small to medium sized [mean = 1.5 mg], testal; embryo long, cylindrical, cotyledon 1, apparently terminal [i.e. bend in embryo axis], 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; (trichoblasts in vertical files, proximal cell smaller); 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); protandry common.
ASPARAGALES + COMMELINIDS: style long; whole nuclear genome duplication [τ/tau event].
COMMELINIDS Back to Main Tree
Unlignified cell walls with ferulic acid ester-linked to xylans [fluorescing blue under UV, green with NH3], flavonolignins + [resinols ± 0]; exodermal cells monomorphic; (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. 4 orders, 30 families, ca 23,500 species.
Age. Estimates of the time when divergence began within commelinids are ca 135 m.y. (Z. Wu et al. 2014), ca 124 m.y. (Tang et al. 2016), ca 122 m.y. (Tank et al. 2015: Table S2), ca 120 m.y. (Janssen & Bremer 2004), (128.7-)118.7(-109.1) m.y. (Eguchi & Tamura 2016), (122-)116(-94) m.y. (Merckx et al. 2008a), ca 116 m.y. (Bremer 2000b), around 112 m.y. (Foster et al. 2016a: q.v. for details), about 108.2 m.y. (Magallón et al. 2015), (113-)103, 96(-86) m.y. (Bell et al. 2010), (104-)99, 91(-86) m.y. (Wikström et al. 2001), ca 83.4 m.y. (Magallón et al. 2013), or only ca 67.1 or 64.5 m.y. (Xue et al. 2012: note topology). Magallón and Castillo (2009: relaxed and constrained penalized likelihood datings) estimate ages of ca 128 and 115 m.y., and ages are (127-)118, 110(-104) m.y. in Hertweck et al. (2015), 93-90 m.y. or 109-97 m.y. in Mennes et al. (2013, 2015 respectively), or around 106 or 83 m.y. in S. Chen et al. (2013).
Note: Boldface denotes possible apomorphies, (....) denotes a feature common in the clade, exact status uncertain, [....] includes explanatory material. Note that the particular node to which many characters, particularly the more cryptic ones, should be assigned is unclear. This is partly because homoplasy is very common, in addition, basic information for all too many characters 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 are the not-so-trivial issues of how character states are delimited and ancestral states are reconstructed (see above).
Evolution. Genes & Genomes. The rate of molecular evolution in commelinids other than Arecales 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 (Orchidaceae), 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 is not that dissimilar to that in these other monocots (S. W. Graham et al. 2006; Barrett et al. 2015b). Was there an increase in the rate of molecular evolution within commelinids, some Poales being spectacular examples?
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. For phytoliths, silica bodies disersed after the plant rots, see Piperno (1991). 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; Nylin et al. 2013). 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. A genome duplication, the τ (tau) duplication, is common to all commelinids examined, but it is perhaps to be pegged to monocots as a whole (Jiao et al. 2014), or at least to the [Asparagales + commelinids] clade (Deng et al. 2015; McKain et al. 2016); it is not known from Alismatales (H. T. Lee et al. 2016; c.f. Olsen et al. 2016).
Chemistry, Morphology, etc. Cell wall ferulates are almost entirely restricted to this clade (Harris & Hartley 1980; Rudall & Caddick 1994), and ferulate polysaccharide esters can be incorporated into lignins (Ralph et al. 1995), however, little is known about cell wall synthesis and the polysaccharides involved (Scheller & Ulvskov 2010; Busse-Wicher et al. 2016). In other angiosperms resinols, β-β-linked units produced by the dimerization of the monolignol sinapyl alcohol, can nucleate lignin chains, whereas here tricin, a flavone, and ferulate serve as nucleating agents, hence flavonolignins (Lan et al. 2015, 2016). For the synthesis of lignins from hydroxycinnamyl alcohols, which can act as the lignin monomers p-coumarate, ferulate and sinapate units, see Ralph (2009); lignins from Poaceae and Arecaceae (and elsewhere?) have p-coumaryl alcohol as well as coniferyl and sinapyl monomers (Seigler 1998).
For the chemistry of the distinctive scallop-shaped epicuticular waxes that are scattered in this area of the monocots (Barthlott & Fröhlich 1983), see Meusel et al. (1994).
Although vessels in the stem and leaves are common (Wagner 1977), this does not appear to be a synapomorphy. For distinctive sieve tubes, see Botha (2013).
The perianth may be quite sharply differentiated into a calyx and corolla, or both whorls may be petal-like, but in either case the inner whorl usually completely surrounds the floral apex and the stamens are borne inside it. 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 here. 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); for silica bodies, see Benvenuto et al. (2015).
Phylogeny. The commelinid clade is well supported in molecular studies (e.g. S. W. Graham et al. 2006 and references; Barrett et al. 2015b) and it has morphological support as well, but support for relationships between the main groups within it has quite often been weak (Chase et al. 2000a; Soltis et al. 2007a). Overall, evidence suggests that Arecaceae are sister to the rest of the clade (but see below), and the 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; Magallón et al. 2015; Hertweck et al. 2015; Barrett et al. 2015b). 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).
Support for the [Commelinales + Zingiberales] clade was sometimes rather weak (e.g. Chase et al. 2000a; Davis et al. 2004: Givnish et al. 2006b, one gene), although it has 100% support in the multi-gene analysis of S. W. Graham et al. (2006) and Chase et al. (2006), good support in the multigene (but poor sampling) study of Soltis et al. (2011) and the plastid genome analysis of Barrett et al. (2015a, b), and it also appears in Hertweck et al. (2015). In some individual analyses in Davis et al. (2004) Commelinales were paraphyletic and included Zingiberales, while Lam et al. (2015) found a moderately supported [Zingiberales + Poales] clade.
The position of Dasypogonaceae has been 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 studies. Some 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]; Magallón et al. 2015 and Foster et al. 2016a: q.v. for details: sister to all other commelinids). More recently, Givnish et al. (2011b, 2016b) and Davis et al. (2011: structural mutations; see also Barrett & Davis 2011; Barrett et al. 2012a, esp. b, 2013, 2015a, esp. b; Ruhfel et al. 2014; Lam et al. 2015) have found some support in various analyses of plastomes for a position of Dasypogonaceae as 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) depicted the relationships [[Arecales [Commelinales + Zingiberales]] [Dasyopogonales + Poales]]. Rudall and Conran (2012) were inclined to think Dasypogonaceae might be included in Poales, partly because both have epidermal silica bodies, where they might be close to Rapateaceae in particular. Indeed, alternative topologies remained possible in some analyses in Barrett et al. (2013), and these included completely novel relationships.
However, analyses of full plastid genomes suggest the relationships [[Dasypogonaceae + Arecaceae] [Poales [Commelinales + Zingiberales]]] (Barrett et al. 2012a, esp. b, 2013, 2015b), those long followed here. 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. Given the predominance of evidence that suggests a [Dasypogonaceae + Arecaceae] clade, an expanded Arecales seems reasonable (see A.P.G. IV 2016).
ARECALES Bromhead Main Tree.
(Stem well-developed, woody); vessels in roots; cuticular waxes as aggregated rodlets; leaves spiral, flowers ± sessile; septal nectaries +; ovule 1/carpel, basal, erect, ?apotropous, outer integument usu. 6< cells across; fruit indehiscent. - 2 families, 192 genera, 2,585 species.
Age. Crown-group Arecales are (114-)109, 102(-98) m.y. (Hertweck et al. 2015) or (122-)112.5(-100) m.y. (Givnish et al. 2016).
Note: Boldface denotes possible apomorphies, (....) denotes a feature common in the clade, exact status uncertain, [....] includes explanatory material. Note that the particular node to which many characters, particularly the more cryptic ones, should be assigned is unclear. This is partly because homoplasy is very common, in addition, basic information for all too many characters 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 are the not-so-trivial issues of how character states are delimited and ancestral states are reconstructed (see above).
Evolution: Divergence & Distribution. 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 (S. A. Smith & Donoghue 2008). Dasypogonaceae are also not exactly fast when it comes to plastome evolution (see also Gaut et al. 1996: comparison between Poaceae and Arecaceae; Comer et al. 2015a: chloroplast genome; Barrett et al. 2015a, esp. b).
Includes Arecaceae, Dasypogonaceae.
Synonymy: Cocosales Nakai, Dasypogonales Doweld
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 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]/18 - two groups below. West Australia, Victoria. [Photo - Habit, Flowers].
Age. Estimates for the age of crown group Dasypogonaceae are ca 100 m.y. (Janssen & Bremer 2004), (78-)68(-56) or (42-)39(-38) m.y. (Hertweck et al. 2015) and (81-)41(-13) m.y. (Givnish et al. 2016b).
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 capitate, 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 +.
2/16. 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
Growth monopodial, stem erect, intracortical roots + [Kingia], or subrhizomatous; SiO2 bodies druse-like; substomatal cells distinctive; leaf bundle girders + [originating in mesophyll]; inflorescence 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, valves 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 (= Asphodelaceae-Xanthorrheoideae s. str.) 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 Asphodelaceae-Xanthorrhoeoideae and Asparagaceae-Lomandroideae, as in Takhtajan (1997: different names).
ARECACEAE Berchtold & J. Presl, nom. cons. // PALMAE Jussieu, nom. cons. et nom. alt. Back to Arecales
Growth monopodial, plant unbranched, erect; flavonoid sulphates abundant; roots lacking real elongation zone, with radially elongated air spaces, root hairs from unmodified rhizodermal cells; vessels also in stem and leaf; sieve tubes with simple sieve plates; sustained growth of the ground parenchyma; no centrifugal differentiation of fibrous phloem cap of fibrovascular bundle; 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; stomata tetracytic; 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; leaves spiral, massive, with petiole and blade, blade developing from the upper part of the leaf, vernation reduplicate-plicate, pinnately pseudocompound, sheath closed; plant monoecious; inflorescence with basal bicarinate prophyll, inflorescence units cincinnus [condensed helical cyme], prophylls lateral; flowers ± sessile, ± small; staminate flowers: A basically trimerous), basifixed; pistillode ± +, nectariferous; carpellate flowers: staminodes +; G (1-4) [2-10], carpels initially free; ovule apotropous, ± sessile, attachment broad, outer integument (4-)6+ cells across, inner integument 2-3(-7 - Ceroxylon/Cocos) cells across, parietal tissue (0)1-5(-6) cells across, (postament +), suprachalazal area ± massive; micropylar embryo sac haustorium +; fruit a drupe; seeds large [>1 cm long], 1(-10)/fruit, rounded; testa usually with two outer layers thickened, (basal portion vascularized); micropylar endosperm haustorium +, endosperm thick-walled, with mannans; cotyledon not photosynthetic, collar short (with roots), primary root strong, branched.
188[list]/2,585 - 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), (103-)83(-85) m.y.a (Givnish et al. 2016b) 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, while there are the very different estimates of (90-)81(-72) and (39-)37(-35) m.y. in Hertweck et al. (2015) and 71-14 or 90-84 m.y. in Mennes et al. (2015, 2015 respectively).
Fossil Arecaceae date to ca 93 m.y. (Pan et al. 2006; Harley 2006).
1. Calamoideae Beilschmied
Plant lianes (not), climbing by ± recurved spiny structures; root periderm 0; 1 (2) vessels/fibrovascular bundle, (centrifugal differentiation of fibrous phloem cap); (sustained growth of the ground parenchyma 0/slight); 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 well-developed; (leaves palmate - Lepidocatyeae); (plant monocarpic); (inflorescence axes adnate to the internode above, or to sheath of the leaf of the next node); plant often dioecious (flowers perfect); C valvate, basally connate, (free); A ≤12; (pollen equatorially disulcate - Calameae); (style branched); funicle twisted [but ovule basically apotropous]; fruit covered by reflexed scales, endocarp thin, (berry - Mauritiinae); seeds 1-3, sarcotesta +, usually thick, (testa thin, dry); n = 13, 14.
21/645. Calamus s.l. (520), Daemonorops (100). Tropical, but esp. Sri Lanka to West Samoa and Fiji (map: from Uhl & Dransfield 1987).
Eugeissoneae W. J. Barker & J. Dransfield
Growth sympodial; fibrovascular bundle with 1(2) vessels, centrifugal differentiation of fibrous phloem cap; endodermal cell walls barely thickened; SiO2 bodies minute, disciform; inflorescence terminal, inflorescence units surrounded by cupule of 7-11 overlapping bracts, monopodial, dyads of staminate and perfect flowers; flowers large [to 9 cm long]; K connate, C woody; stamens 20-70, development centrifugal; nectar also produced from ventral slits of the carpels; micropyle bistomal, outer integument 50-60 cells across, inner integument ca 10 cells across; fruit scales small; mesocarp forming lignified stony layer, ridged, endocarp massive, becoming crushed; seeds longitudinally ruminate; n = ?; plastid ndhF gene 0.
1/6. S. Thailand to Borneo (Map: from Dransfield et al. 2008b).
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 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), which allows the imagination plenty of freedom.
2. Nypoideae Griffith
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; plant monoecious; inflorescence racemose, staminate inflorescence a spike, carpellate inflorescence a head, axis adnate to the internode above; P free, ± undifferentiated; staminate flowers: A 3, opposite outer P, connate, synangial stalk solid, anthers extrorse; pollen with encircling sulcus [meridionosulcate], surface spiny; 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 and Spalding et al. 2010; fossil records from places outside this area in blue, from Plaziat et al. 2001, note that Nypa-like pollen is known from the Late Cretaceous in Patagonia - Barreda et al. 2012).
Synonymy: Nypaceae Le Maout & Decaisne
[Coryphoideae [Ceroxyloideae + Arecoideae]]: sieve tube with compound sieve plates; (sustained growth of the ground parenchyma 0); 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), while estimates are (98-)51(-15) m.y. in Merckx et al. (2008a), 86.3-83.6 m.y. in Iles et al. (2015: fossils, stem node age of Coryphoideae) and (100.1-)90.7(-85) m.y. in Eguchi and Tamura (2016: c.f. comparisons).
3. Coryphoideae Burnett
(Stem branched - e.g. Caryota); septate fibres +; (1 vessel/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), vernation often induplicate-plicate; inflorescence various, (terminal; adnate to the internode above; flowers perfect, (plant monoecious - Caryoteae), (dioecious - Borasseae), flowers solitary or in cincinni (triads), (large - Lodoicea); C often valvate, connate (free); microsporocyte with callose ring [not Caryota, Bismarckia]; G (1), free or postgenitally connate by stigmatic zone, style 0 [Caryoteae], or +, with 3 [Coryphinae] or 1 [Sabalinae] stylar canals.
47/505: 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]: centrifugal differentiation of fibrous phloem cap of fibrovascular bundle (not); petiole bundles arranged in one or more Vs (scattered); sheaths of transverse veins sclereidal, veins sinuous, irregular, epidermal cells hexagonal to spindle-shaped.
Age. The age of this node is around 78 m.y. (Iles et al. 2015: check).
4. Ceroxyloideae Drude
(Often ≥3 vessels/fibrovascular bundle); plant usu. dioecious, (flowers perfect); inflorescence racemose, spicate; flowers single, (large - Phyelepheae); (K and C elongate), (free); (A not trimerous, very many, with trunk bundles, development centrifugal - Phytelepheae), (development centripetal - Ceroxylon); G [3-10], receptacle elongated; (seeds more than 3).
8/47. 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]), (basipetal hapaxanthy - Caryoteae); 1 vessel/fibrovascular bundle (1(2) vessels); (SiO2 bodies hat-shaped); hypodermal cells hexagonal, transversely elongate; plant usu. monoecious; flowers in triads [central (upper) flower carpellate, lateral flowers staminate] or in two vertical rows [acervuli: Chamaedoreeae], (inflorescences spicate); (flowers protandrous); (C valvate); (A 3); (1 G fertile), style branches separate, (style single, short or long); (inner integument ca 7 cells across - Cocos); n = 16.
111/1390: Bactris (240), Dypsis (165), Pinanga (120), Chamaedorea (110), Geonoma (70), Syagrus (65), Areca (60), Desmoncus (?12/65<), 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 leaves, pollen and/or wood are quite common and widely distributed in the later Cretaceous when global temperatures were warmer (Burnham & Johnson 2004; Nichols & Johnson 2008: pollen; Friis et al. 2011), including in Africa and India where palms are not very diverse today. Palma were also widely distributed in the earlier Caenozoic (e.g. Greenwoood & West 2016), and palm pollen is recorded from palaeo 85o N sediments dated to 53.5 m.y.a. in the Eocene on the Lomonosov Ridge (Sluijs et al. 2009) and from palaeo 70o S sediments dated to ca 51.9 m.y.a. in the Eocene off Wilkes Land in the Antarctic (Pross et al. 2012). However, by the Oligocene extra-tropical climates were becoming more seasonal, and so less favourable for palms away from lower latitudes. Fossils (leaf, stem, fruit) from Cretaceous-Campanian rocks in Texas around 77 m.y.o. from Texas have been identified as the modern genus Sabal, and young dinosaurs might perhaps have eaten their fruits (Manchester et al. 2010a); dinosaurs aside, if the identification is correct, some ages for the family and Coryphoideae, to which Sabal belongs, are not correct. For similar problems over dating Cocos and relatives, see below. Iles et al. (2015) provide dates for well-attested palm fossils.
For diversification in Arecaceae, see Faury et al. (2016). It has been suggested that Arecaceae have diversified at a constant rate since their origin in the Cretaceous ca 100 m.y. or more ago (perhaps in Laurasia) until ca 24 m.y.a., the K/C boundary passing unmarked (Couvreur et al. 2011b, esp. c). Palms then might serve as markers for tropical rain forest or a rain forest-like biome (Couvreur et al. 2011b). This being said, the early evolution of the rain forest biome is still not well understood (see elsewhere). Thomas and Boura (2015 and references) found the fibro-vascular bundles with two vessels per bundle were common in palms like Coryphoideae that lived in places with a dry period, and such bundles, but not one-vessel bundles, common in rain forest-dwelling Arecoideae, for example, are found in palm fossils of Cretaceous age. Coiffard and Gomez (2009) even suggest that early palms may have been swamp dwellers like living basal Arecaceae (they listed Calamus, Nypa, and Mauritia). As with other angiosperms, palms are not very diverse in Africa, and Faye et al. (2016) suggested that in the Calamoideae that they were studying there may have been an extinction event at the Eocene-Oligocene boundary.
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 Caenozoic, 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.
There is much debate as to where and when Cocos (Arecoideae) originated. Crown-group Cocoseae are estimated to be around 63.8 m.y.o.; nothing much happened divergence-wise for the next ca 25 m.y. (Meerow et al. 2014). Gunn (2004) suggested that Cocos might be sister to the New World Parajubaea (see also Baker et al. 2009; Faurby et al. 2016) and be at least 22 m.y.o., 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). Note that general relationships in this part of the tree are unclear (c.f. Baker et al. 2009 and Faury et al. 2016). Furthermore, fruits in Late Cretaceous Deccan Intertrappean Beds 65.5-61.7 m.y.o. are reported to be those of Cocos (Srivastava & Srivasatava 2014) and Gómez-Navarro et al. (2009) found fruits that they compared with Cocos from northern Colombia that are only a little younger - about 58 m.y.o, while fruits ca 62 m.y.a. from Argentina have been identified as Arecoideae-Cocoseae-Attaleinae (Futey et al. 2012). Something is very wrong somewhere.
Despite the size of many palms and of their fruits, dispersal rather than vicariance is increasingly frequently being invoked to explain many apects of present distributions within the family (Bacon et al. 2012; Baker & Couvreur 2012). The scattered and apparently ancient Gondwanan distribution of Ceroxyloideae is probably best explained by several mid-Caenozoic trans-oceanic dispersal events (Trénel et al. 2007). For diversification within Arecoideae, see Comer et al. (2015b). 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 there. Madagascan palms lack spines, etc., unlike their African relatives, perhepas because of the absence of large herbivores on the island (Dransfield & Rakotoarinivo 2011). On the African mainland palms became less common at the beginning of the Caenozoic 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 relative paucity of palms on the continent can perhaps be explained by the increase in diversification rates elsewhere (Bacon et al. 2012) and also because African palm diversity is the historical legacy of past climatic events (esp. since the Late Miocene ca 10 m.y.a.) that is evident in their present restricted distributions (Blanch-Overgaard et al. 2013).
The diversity and diversification of palms in the New World and the Indo-Malesian area 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. 2012). 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. (2012), Baker and Couvreur (2012, 2013a, b), Couvreur et al. (2015), 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 (see also Roncal et al. 2012 for the evolution of Geonoma, but "characters" here are curious constructs). 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 Malesian-centred Calamus, with some 400 or more species, is only 24 m.y.; the climbing habit in calamoid palms, which has originated more than once, is associated with increased diversification rates, although some less diverse clades are hapanxanthic, an odd feature to find in lianas (Couvreur et al. 2015; Marazzi et al. 2012 for tendencies - the several origins of the climbing habit in Calamoideae). For diversification in S.E. Asian/Malesian palms, see Baker and Couvreur (2012) and Bacon et al. (2013). Kristiansen et al. (2012) looked at palm communities in western Amazonia in the context of the dispersal abilities of the species and their ecological preferences - ± canopy, understorey.
Horn et al. (2008, 2009b, 2010a, esp. 2009b) and especially Tomlinson et al. (2011) look at various aspects of lamina anatomy and Thomas and Boura (2015) some stem anatomy in the context of the phylogeny of the family. Their work has in part been integrated above, but there is widespread homoplasy in the characters. 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 plants 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 (Couvreur et al. 2011c; 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). Palms make up 7/8 of the monocots in the top 20 in terms of stem numbers in Amazonian forests (Fauset et al. 2015), and genera like Chamaedorea are particularly common in the understory.
Palms can be very conspicuous components of the vegetation. Nypa dominates some mangrove habitats, although 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. 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 Amazonian 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 mostly 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; physiologically functional cells must 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; sustained growth of the ground parenchyma - Thomas & Boura 2015; 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 (references in Angyalossy et al. 2012).
Calamoid palms are a very important group of lianes in the South East Asian rain forests (Gentry 1991), elsewhere palm lianes are uncommon, althouth Desmoncus is a New World liane; there are about 535 species of climbing palms all told. When the climbing habit evolved is unclear, perhaps early Eocene to Miocene (Couvreur et al. 2015). Various features of these palms might have made them successful: All have thin woody stems and climbing is effected by spines, often recurved and either on leaves and/or modified inflorescences, the latter only in Calamoideae (Couvreur et al. 2015). 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). Such vessels would appear to be susceptible to cavitation, but 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, but c.f. Knipfer et al. 2016: living tissues control cavitation in grapes, at least; Schenk et al. 2017: lipid surfactants in the xylem help prevent the formation of embolisms). Tomlinson (2006b) thought of rattan xylem function in the context of stem length; Rowe and Speck (2015) discuss biomechanical aspects and Isnard and Feild (2015) morphological-functional aspects of being a climbing palm (see also below). Raphia laurentii (Lepidocaryeae) is one of the four common species mentioned growing in the ca 145,500 km2 of peat in the Cuvette Centrale in the Congo (Dargie et al. 2017).
Thomas and Boura (2015) examined various aspects of stem anatomy of palms in the context of their ecology. They found the fibro-vascular bundles with two vessels per bundle were common in palms that lived in places with a dry period, and these palms include half of all Coryphoideae. Such two-vessel bundles, but not one-vessel bundles, common in rain forest-dwelling Arecoideae, for example, are known from palm fossils of Cretaceous age (Thomas & Boura 2015 and references).
Arecoid palms in particular are an important food resource for specialized frugivorous birds in the New World (Snow 1981; Staggemeier et al. 2017).
Pollination Biology & Seed Dispersal. Pollination is predominantly by insects, whether beetles (mainly Nitidulae, cyclocephaline scarabs, Curculionidae-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; Knudsen et al. 2001; Barfod et al. 2011; Moore & Jameson 2013). There is no clear correlation of pollen morphology with pollinator (Sannier et al. 2009) nor of floral scent with taxonomy (Moore & Jameson 2013). Mystrops, a nitidulid, is a common pollinator of palms, and shows quite a degree of host specificity, at least locally (Restrepo Correa et al. 2016). 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, including the beetle-pollinated Ceroxyloideae-Phytelepheae, mostly in flowers lacking nectar (Silberbauer-Gottsberger 1990; Seymour 2001; Knudsen et al. 2001). Beetles may lay eggs in staminate inflorescences (Silberbauer-Gottsberger 1990), and there are several records of cyclocephaline scarabs visiting palm flowers (Moore & Jameson 2013). Mimicry oby female flowers of male flowers, the latter only offering rewards, is reported (Knudsen et al. 2001). There may be mimicry by female of male flowers in Geonoma (Stauffer et al. 2002); for floral scent in geonomoid palms, see Knudsen (1999). The calamoid Eugeissona tristis produces considerable amounts of fermented nectar (to ca 3.8% alcohol) in its very large, robustly-constructed and long-lived flowers (Stauffer et al. 2016), and small pen-tailed tree shrews, its pollinators, and other animals quaff the nectar without any damage to themselves or the plant; the beginning of this association has been dated to some 55 m.y.a. (Wiens et al. 2008).
There is a great variety of breeding systems in the family, although particular systems tend to predominate in each subfamily; protandry is common, or, in monoecious taxa, the male flowers open first (Nadot et al. 2016).
The speciose New World Chamaedoreeae (Arecoideae) all have raphides in the flowers and in Chamaedorea these are particularly common in the perianth and gynoecium; for these and other potentially protective structures in the flowers, see 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 the cocnut, Cocos nucifera, dispersed by sea currents, is a notable exception (Zona & Henderson 1989; Henderson 2002). Dispersal of some Malagasy palms may now be compromised because of the recent extinctions of all the largest frugivorous lemurs and the elephant bird and its relatives (Federman et al. 2016).
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, groups like Elymnini , Amathusiinae and Morphini being well represented here (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). For other palm-insect associations, see papers in Trucchi et al. (2003).
Myrmecophily in the family has been little studied, but some 50 species of rattans are myrmecophilous (Dransfield 2003). Ants live in domatia formed by the ocrea (= ligule) which either ensheath the stem or stand at an angle to it (Merklinger et al. 2014 for their development), or whorls of spines along the stem may form the scaffolding for ant nests, nests of adjacent whorls being connected by carton-covered runways (Rickson & Rickson 1986; Dransfield 2003: carton made up of rattan scales and hairs and ant saliva), or the ants may live in leaflets that are held close to the stem, inside imbricate inflorescence bracts, etc. (e.g. Dransfield 2003; Sunderland 2004: African rattans). Plant debris accumulates in the leaves of the rattan Daemonorops in Pasoh, the Malay Peninsular, and the leaves rot, nutrients being washed down the stem and then perhaps being absorbed by the carton of ant nests, from which nutrients move into the palm (Rickson & Rickson 1986; c.f. Dransfield 2003: secondary consequence?). In some cases the ant (Camponotus spp.) exists on honeydew produced by the hormaphid Cerataphis which the ant actively tends, for instance moving the aphids as the colony expands; this aphid is also to be found on palms other than rattans and also inside galls on its primary host, Styrax benzoin (Mattes et al. 1998; see also Chan et al. 2012). Camponotus - depending on the species - appears to protect the rattan Korthalsia against herbivory and also remove epiphylls (Edwards et al. 2019; Miler et al. 2016: no mention of aphids in either case). The specificity of these ant-rattan associations is unclear (see Rickson & Rickson 1986; Mattes et al. 1998; Sunderland 2004; Chan et al. 2012), and since there was no "sanctioning" by the plant of ants that were of no benefit to it, Edwards et al. (2010) suggested that cheaters could occupy the domatia of K. furtadoana, at least - an idea to be checked.no
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..
Vegetative branching in such situations is unlikely, although dichotomous branching of one sort or another is scattered in the family, having first been recorded from Hyphaene thebaica with its distinctively-branched aerial trunks by Schoute in 1909 (Fisher 1974 and references; see also Fisher & Maidman 1999). There are other forms of vegetative branching, and of course axillary branching that produces inflorescences is the norm. In some rattans (Calameae) the axillary bud is displaced onto the sheath of the next youngest leaf, where it is evident as an inflorescence or cilium (Fisher & Maidman 1999).
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. There is differential growth in the blade, and 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 (e.g. Desmoncus), are climbers, all told around 535 species (Couvreur et al. 2015), and climbing is either by a long, hook-bearing apical portion of the leaf, the cirrus, and also, in Calamus and relatives, a very much modified long and very thin inflorescence axis with recurved spines, the cilium, that is basally 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 cilium, 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 and Rowe (2008 and references) give details of the biomechanics of climbing of these palms. Some ant-associated rattans (see above) have an ocrea, basically a souped-up ligule as long as 1.5 m that functions as an ant domatium, that develops at the junction of the leaf sheath and petiole (see Merklinger et al. 2014 for its development).
Genes & Genomes. A genome duplication in Phoenix dated to (57.8-)53.7(-48.5) m.y.a. (Vanneste et al. 2014a) could involve quite a lot of the family (see also D'Hont et al. 2012; McKain et al. 2016).
For plastome evolution in the family, see Barrett et al.( 2015a, esp. b).
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). For genome size in coconuts and their relatives, see Gunn et al. (2015). The coconut hispine beetle Brontispina longissima - its relatives eat other commelinids - is a serious pest.
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. 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).
Caryoteae quite often have basipetal hapaxanthy, a feature ethat has been used to suggest that the group is a subfamily (Dransfield & Mogea 1984). 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); in Arecaceae, the cincinnus seems to be the basal inflorescence units from which others have been derived (see also Castaño et al. 2014; Comer et al. 2015b). The flowers 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. For floral development in monoecious and dioecious taxa in Arecoideae-Chamaedoreeae, see Castaño et al. (2016). 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. Indeed, quite a number of taxa have flowers with only a single fertile carpel, and then the style is gynobasic ((Stauffer et al. 2002 and references). 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) and Thadeo et al. (2015); Dransfield et al. (2008b) note that the stony layer of Eugeissona differs from that of other Arecaceae. Mannans, rseerve celluloses, are common in (?throughout) Arecaceae where they are to be found in the endosperm, immature seeds have legume-like galactomannans (Kooiman 1871; Reid 1985). In Voaniola n = 298 or more.
We are fortunate in having a series of major works devoted to palms, including von Martius's (with 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, considerable variation), 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), Balhara et al. (2013: Ceroxylon), Castaño et al. 2014: Gaussia) and Stauffer et al. (2016: Eugeissona), all floral morphology/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), Essig (2008), Romanov et al. (2011) and Reis et al. (2017), all fruit anatomy, Zona (2004: embryo raphides), and Henderson (2006: detailed descriptions of germination, not integrated with phylogeny).
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], but support was weak in Comer et al. (2015b). However, Calamoideae have been found to be 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 even in 2006 might have seemed 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, and more recently by Barrett et al. (2015a, esp. b: support for monophyly and position of all subfamilies strong) and Faurby et al. (2016: again Nypa is a little perambulatory...).
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. However, this position was not recovered by Baker et al. (2009), while in the species-level supertree of Faurby et al. (2016) Eugeissona was sister to a [Korthalsia + Retispatha, etc.] clade. For relationships in African rattans, see Faye et al. (2016).
Coryphoideae include Caryoteae, previously placed in Arecoideae (Uhl & Dransfield 1987; see also Dransfield et al. 2008a for a phylogeny). A number of taxa have diversified on islands, and Bacon et al. (2012) discussed the relationships of several genera of these in Trachycarpeae. Relationships in Faurby et al. (2016) are [[syncarpous clade] [Sabal [Crysophileae [Trachymeneae + Phoenix]]]], however, Sabal and Phoenix had switched positions compared with Baker et al. (2009) - remember the Cretaceous fossil Sabal (see above) - and within the syncarpous clade Corypha moves around.
Ceroxyloideae include Phytelephatoideae (Dransfield et al. 2005); for relationships, see Faurby et al. (2016). 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, see also 2006, 1009) examined phylogenetic relationships within Arecoideae; tribes were monophyletic, but relationships within the large Areceae were unclear (see also Lewis & Doyle 2002; especially Faurby et al. 2016). Relationships within the subfamily in a plastome analysis by Comer et al. (2015a) are [Chamaedorea [Iriartea + The Rest]], and there was a fair bit of resolution; looking at the whole chloroplast genome got over the rather small signal in individual chloroplast genes, the chloroplast genome evolving rather slowly. Although Comer et al. (2015b) found that the position of the two genera above reversed in a nuclear phylogenomic study, branch lengths here are short (but see also Faurby et al. 2016: as tribes). For a phylogeny of the South American Iriarteeae, see Bacon et al. (2016); the distinctive clustered inflorescences of some species of Wettinia have evolved several times in parallel. 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%. Cocos was sister to Attalea in most analyses of variation in the WRKY gene family (Meerow et al. 2014). Both Baker et al. (2009) and Faurby et al. (2016) found that Cocos and Parajubaea were sister taxa, although they disagreed over relationships immediately beyond this. Eiserhardt et al. (2011a) discussed phylogenetic relationships in the spiny Neotropical Bactridinae, which includes the climbing Desmoncus. Cuenca and Asmussen-Lange (2007) and Cuenca et al. (2007, 2008) looked at 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). For the difficult genus Geonoma, within which it was difficult to get much resolution, and the Geonomateae, see Roncal et al. (2012 and references).
Classification. Dransfield et al. (2008b, see also Dransfield et al. 2005) present the classification followed here. 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.
For an expanded circumscription of Calamoideae-Calamus, see Baker (2015).
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, but c.f. Furcraea (Asparagaceae) in terms of length); the largest seed - Lodoicea maldavica, to 50 cm long and 15-30 kg - which in turn produces the longest cotyledon (strictly speaking, an apocole, the 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 that can remain functional for hundreds of years (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 been germinated (Sallon et al. 2008; see also Kew Magazine, Winter 2008: 28-31).