EXTANT SEED PLANTS

Plant woody, evergreen; nicotinic acid metabolised to trigonelline; primary cell walls rich in xyloglucans and/or glucomannans, 25-30% pectin [Type I walls]; lignins rich in guaiacyl units; true roots present, apex multicellular, xylem exarch, branching endogenous; arbuscular mycorrhizae +; shoot apical meristem multicellular; stem with ectophloic eustele, endodermis 0, xylem endarch, branching exogenous; vascular tissue in t.s. discontinuous by interfascicular regions; vascular cambium + [xylem ("wood") differentiating internally, phloem externally]; wood homoxylous, tracheids +; tracheid/tracheid pits circular, bordered; sieve tube/cell plastids with starch grains; phloem fibers +; stem cork cambium superficial, root cork cambium deep seated; nodes ?; stomata ?; leaf vascular bundles collateral; leaves spiral, simple, axillary buds?, prophylls [including bracteoles] two, lateral, veins -5 mm/mm² [mean for all non-angiosperms 1.8]; plant heterosporous, sporangia eusporangiate, on sporophylls, sporophylls aggregated in indeterminate cones/strobili; true pollen [microspores, i.e. no distal pore for release of gametes] +, grains mono[ana]sulcate, exine and intine homogeneous, ovules unitegmic, crassinucellate, megaspore tetrad tetrahedral, only one megaspore develops, megasporangium indehiscent; male gametophyte development first endo- then exosporic, tube developing from distal end of grain, to ca 2 mm from receptive surface to egg, gametes two, with cell walls, with many flagellae; female gametophyte endosporic, initially syncytial, walls then surrounding individual nuclei; seeds "large", first cell wall of zygote transverse, embryo straight, endoscopic [suspensor +], short-minute, with morphological dormancy, white, cotyledons 2; plastid transmission maternal; two copies of LEAFY gene, PHY gene duplication [N/O//A/C and P//BE lines], mitochondrial nad1 intron 2 and coxIIi3 intron present.

MAGNOLIOPHYTA

Plant woody, evergreen; lignans, O-methyl flavonols, dihydroflavonols, triterpenoid oleanane, non-hydrolysable tannins, quercetin and/or kaempferol +, apigenin and/or luteolin scattered, cyanogenesis via tyrosine pathway [ANITA grade?], lignins derived from both coniferyl and sinapyl alcohols, containing syringaldehyde [in positive Maüle reaction, syringyl:guaiacyl ratio less 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; stem with 2-layered tunica-corpus construction; wood fibers and wood parenchyma +; reaction wood ?, with gelatinous fibres; starch grains simple; primary cell wall mostly with pectic polysaccharides; tracheids +; sieve tubes eunucleate, with a sieve plate and cytoplasm with P-proteins, companion cells from same mother cell that gave rise to the sieve tube; nodes unilacunar [1:?]; stomata with ends of guard cells level with pore, paracytic, outer stomatal ledges producing vestibule; leaves with petiole and lamina [the latter formed from the primordial leaf apex], development of venation acropetal, 2ndary veins pinnate, fine venation reticulate, veins (1.7-)4.1(-5.7) mm/mm², endings free; flowers perfect, polysymmetric, parts spiral [esp. the A], free, development in general centripetal, numbers unstable, P not differentiated, outer members not enclosing the rest of the bud, smaller than inner members, A many, with a single trace, introrse, filaments stout, anther ± embedded in the filament, tetrasporangiate, dithecal, with at least outer secondary parietal cells dividing, each theca dehiscing longitudinally by action of hypodermal endothecium, endothecial cells elongated at right angles to long axis of anther, tapetum glandular, binucleate, microspore mother cells in a block, microsporogenesis successive, walls developing by centripetal furrowing, pollen subspherical, binucleate at dispersal, trinucleate eventually, tectum continuous or microperforate, ektexine columellar, endexine thin, compact, lamellate only in the apertural regions, pollen germinating in less than 3 hours, tube elongated, growing at 80-600 µm/hour, with callose plugs and callose-based walls, penetrating between cells, siphonogamy, penetration of ovules within ca 18 hours, distance to first ovule 1.1.-2.1 mm, nectary 0, G free, several, ascidiate, with postgenital occlusion by secretion, few [?1] ovules/carpel, ovules marginal, anatropous, bitegmic, [outer integument often largely subdermal in origin, inner integument dermal], micropyle endostomal, integuments 2-3 cells thick, megasporocyte single, megaspore lacking sporopollenin and cuticle, chalazal, female gametophyte four-celled [one-modular, nucleus of egg cell sister to one of the polar nuclei], stylulus short, hollow, stigma ± decurrent, dry [not secretory]; P deciduous in fruit; seed exotestal; double fertilisation +, endosperm diploid, cellular [first division oblique, micropylar end initially with a single large cell, chalazal end more actively dividing], copious, oily and/or proteinaceous, embryo cellular ab initio, minute; germination hypogeal, seedlings/young plants sympodial; Arabidopsis-type telomeres [(TTTAGGG)_n]; whole genome duplication, 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 PHYA + C/PHYB + E gene pairs.

Possible apomorphies are in bold. Note that the actual level to which many of these features, particularly the more cryptic ones, should be assigned is unclear, because some taxa basal to the [magnoliid + monocot + eudicot] group have been surprisingly little studied, there is considerable variation between families in particular for several of these characters, and also because details of relationships among gymnosperms will affect the level at which some of these characters are pegged.

NYMPHAEALES [AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]: vessels +, elements with scalariform perforation plates; ?genome duplication; "DEAER" motif in AP3 and PI genes lost, gaps in these genes.

MONOCOTS [CERATOPHYLLALES + EUDICOTS]: (veins in lamina often 7-17mm/mm² or more [mean for eudicots 8.0]; stamens opposite [two whorls of] P; pollen tube growth fast).   Back to Main Tree

Evolution. Chaw et al. (2004: 61 chloroplast genes, sampling poor) date this node to 150-140 million years ago.

Chemistry, Morphology, etc. Details of the exact position and magnitude of changes in characters like leaf venation density and pollen tube growth are still provisional (see Boyce et al. 2008; Williams 2008 for more details). The stamen-perianth member pairing, as well as the fact that the bases of members of a perianth whorl do not completely surround the floral apex, are two features very common in monocots, but they are rather more scattered in the eudicot clades up to Gunnerales, after which it is pretty much non-existent. Lauraceae may also be interpreted as having this sort of flower (see also below).

Phylogeny. The topology of the main tree in this area is rather different from that in earlier versions of A.P.G. (1999, 2003). For further information, in particular see the discussion immediately preceding Magnoliales, i.e. the magnoliid clade; also see Ceratophyllales, Chloranthales, and eudicots are the other clades involved.

MONOCOTYLEDONS  Back to Main Tree

Herbaceous, rhizomatous, plant sympodial; non-hydrolyzable tannins [(ent-)epicatechin-4] +, ellagitannins, neolignans, benzylisoquinoline alkaloids 0, hemicelluloses as xylans; root apical meristem?; root epidermis developed from outer layer of cortex; trichoblasts in vertical files with proximal cell smaller or hypodermal cells dimorphic; cork cambium in root [uncommon] superficial; root vascular tissue oligo- to polyarch, medullated, lateral roots arise opposite phloem poles; primary thickening meristem +; vascular bundles in stem scattered, (amphivasal), closed [no interfascicular cambium developing]; vessel elements in root with scalariform and/or simple perforations; tracheids only in stems and leaves 0; sieve tube plastids with cuneate protein crystals alone; stomata paracytic [divisions of neighbouring cells oblique]; leaves not differentiated into petiole plus lamina, main venation parallel, developing both acropetally and basipetally from the base and converging towards the apex, intermediate [and other] veins basipetal from apex, endings not free, (margins with spiny teeth), Vorläuferspitze +, base sheathing, sheath open, colleters [intravaginal squamules] +; inflorescence racemose; flowers 3-merous, polysymmetric, pentacyclic, T in two whorls, each member with three traces, median member of outer whorl abaxial, members of whorls alternating, similar, [pseudomonocyclic, each providing a sector for the T tube when present], stamens = and opposite each T member [primordia often associated, and/or A vascularised from tepal trace], anther and filament more or less sharply distinguished, anthers subbasifixed, G [3], development?, opposite outer tepals [thus median member abaxial], placentation axile, outer integument often largely dermal in origin, antipodal cells persistent, proliferating; fruit a loculicidal capsule; seed testal; embryo long, cylindrical, cotyledon 1, terminal, plumule lateral; primary root unbranched, not very well developed, adventitious roots numerous, hypocotyl short, (collar rhizoids +), cotyledon with a closed sheath, unifacial [hyperphyllar], both assimilating and haustorial; duplication producing monocot LOFSEP and FUL3 genes, [latter duplication of AP1/FUL gene], PHYE gene lost. - 11 orders, families, 60,100 species.

Some features that are likely to be synapomorphies are in bold. If Ceratophyllaceae were sister to monocots, synapomorphies like the herbaceous habit, absence of vascular cambium, etc., could be moved down a node, but currently there is little evidence for such a likelihood (). Note that over half the putative synapomorphies in Table 4.1 of Soltis et al. (2005b) are in fact unlikely to be synapomorphies. The nature of the anther-filament junction has not been optimised in this part of the tree.

Evolution. The oldest unequivocally monocotyledonous fossils (as pollen) are from the Late Barremian-Early Aptian of the Cretaceous some 120-110 million years ago and are assignable to Araceae-Pothoideae-Monstereae; Araceae are sister to other Alismatales (Friis et al. 2004: for fossil monocots, cf. Gandolfo et al. 2000 and Friis et al. 2006b). The age of the crown monocots has been variously estimated at ca 200±20 million years before present (Savard et al. 1994), 160±16 million years before present (Goremykin et al. 1997), 135-131 million years (Leebens-Mack et al. 2005), 133.8-124 million years (Moore et al. 2007), etc. Bremer (2000b) suggested that the split between Acorales and other monocots could be dated to ca 134 million years before present (147-121 million years before present), a date also used in a more recent and comprehensive analysis that formed the basis for dating the age of monocot groups in general (Janssen & Bremer 2004).

Caterpillars of skipper butterflies of the Castniidae are found on a variety of monocots (Forbes 1956; Powell et al. 1999 for some other groups that prefer monocots). Larvae of the chrysomelid beetle group Galerucinae subribe Diabroticites are apparently quite common on monocots, where they feed on roots (Eben 1999), indeed, Hispinae-Cassidinae (6000 species), sister to Galerucinae (10,000 species) are the major group of monocot-eating beetles (Jolivet & Hawkeswood 1995; Wilf et al. 2000; Chaboo 2007). Wilf et al. (2000) thought that these beetles initially ate aquatic members of Acorales and Alismatales, the association of commelinids with Hispinae-Cassidinae being derived, but Gómez-Zurita et al. (2007) suggest that the two main clades of monocot-eating chrysomelid beetles are unrelated, and also that the chrysomelids diversified 86-63 million years ago, well after the origin of monocots. The idea has been floated that monocots experience less herbivory in tropical lowland rainforests than do other angiosperms, in part because they are tough and in part because the leaves remain rolled up for a relatively long time (Grubb et al. 2008); many monocots also have raphides as their main crystalline form of calcium oxalate, and these may be involved in herbivore defence (e.g. see Araceae; Franceschi & Nakata 2005). Monocots are practically never ectomycorrhizal.

It has long been noted that many of the distinctive features of monocots are compatible with an origin from aquatic or hydrophilous ancestors (e.g. Henslow 1893 and references: the style of comparison and suggested mechanisms are interesting!). The scattered vascular bundles in the stem, long linear leaves, absence of secondary thickening (all perhaps related to the biomechanics of living in water), clusters of roots, rather than a single, branched tapwoot (see nature of substrate - mud), even the sympodial habit, etc., are all compatible with such an origin. Many members of the first two pectinations in the monocot tree, Acorales and Alismatales, are water or marsh plants or at least prefer to grow in damp conditions, but even if monocots were sister to the aquatic Ceratophyllales (which see for literature) and/or their origin can be linked to the adoption of some kind of aquatic habitat, it does not help much in our understanding of the evo-devo side of how the distinctive monocot anatomical features, etc., evolved. Monocots appear to be so different from other angiosperms that relating their morphology, anatomy and development to that of broad-leaved angiosperms is difficult (e.g. Zimmermann & Tomlinson 1972; Tomlinson 1995). Nymphaeales and Ceratophyllales are scarcely less remarkable in this respect, but the common ancestors of all these clades with broad-leaved angiosperms is likely to have been plants with broad, petiolate leaves and a woody stem with lateral thickening meristems (cork and vascular cambiums).

Scattered through the group are taxa with broad, net-veined leaves and also fleshy fruits (excluding things like arillate, ant-dispersed seeds), both adaptations to shady conditions, features that have tended to evolve together but independently (Dahlgren & Clifford 1982; Patterson & Givnish 2002; Givnish et al. 2005, 2006b). A number of these plants are vines, which often live in shady habits for at least parts of their lives, and there may also be an association with unoriented stomata (see Cameron & Dickison 1998 for references for the latter feature). Givnish et al. (2005, 2006b) recently suggested that net venation has arisen at least 26 times in monocots, fleshy fruits 21 times (they were sometimes subsequently lost); the two features, although independent, showed very strong signs of tending to be gained or lost in tandem, a phenomenon they describe as "concerted convergence".

Chemistry, Morphology, etc. Some monocots (Amaryllidaceae, Araceae) have benzylisoqinoline alkaloids, but it is unclear if they are produced by the same biosynthetic pathway as these alkaloids in broad-leaved angiosperms (Waterman 1999). Many monocots are sympodial (Holttum 1955) and form tufts of leaves in part of each growth cycle, and/or are geophytes; internode elongation in such cases is very slight. Cork cambium in the roots is superficial in origin, developing just beneath the exodermis (Arber 1925); I am unclear as to how common it really is, at best it seems rare. Given that a vascular cambium in monocots is uncommon, yet many are plants of quite considerable stature, even tree-like, there must be considerable changes in the plant in the period between germination and the mature (flower-producing) stage, particularly in the size of the apical meristem. This period is often designated as establishment growth (e.g. Tomlinson & Esler 1972; Bell & Bryan 2008). Vascular bundles in some monocots may have a sort of cambial layer, but it never amounts to much (Arber 1919). Cheadle (e.g. 1944) and Wagner (1977) surveyed vessel types in the vegetative parts of monocots; although there appear to be large-scale patterns, these data need to be extended; Cheadle (1944) noted that there could be substantial variation in vessel morphology between closelly related (congeneric) species. Amphivasal vascular bundles are common in monocot stems, although they are absent in some groups (e.g. Jeffrey 1917; Arber 1925). Botha (2005) discusses distinctive thick-walled late-formed sieve tubes that lack companion cells that are to be found only in monocot vascular bundles (but the sampling is not that good); they are found close to the tracheary elements in the bundles. Paracytic (and tetracytic) stomata are common in monocots, and variation in how they develop may characterise major clades (Poales + Commelinales + Zingiberales: cf. Tomlinson 1974, which, however, see for data - of which more are needed: Rudall 2000). Although it has been suggested that there are only two tunica layers in monocots, it is perhaps not surprising that the tissues in the leaves are derived from three types of cells, as in other angiosperms (Stewart & Dermen 1979); the inner layer in monocots may, however, come from the corpus rather than a tunica layer. The outer tunica layer can proliferate and produce a rather broad margin to the variegated leaf. Zonneveld (2007) suggests that stomata occur in general epidermal cells in monocots, but not in other angiosperms; I have been unable to confirm this observation. Monocot leaf teeth, when present, are more or less spinose, never glandular. Colleter-like structures ("intravaginal squamules") may be a synapomorphy of monocots or of independent origins in Acorales and other Alismatales, within Araceae, for instance, they seem to be known only from very much embedded genera such as Philodendron, Cryptocoryne and Lagenandra (M. Carlsen, pers. comm.; see also Wilder 1975). When the leaf is differentiated into petiole and lamina, ptyxis refers only to the latter.

The development of monocot leaves needs much more study. Although a Vorläuferspitze - a usually small abaxial conical or cylindrical protrusion at the apex of the mature leaf, and representing the upper part of the leaf - is common, it may be that in Acorales and Alismatales in particular the blade develops from this upper part of the leaf primordium. As a result they would be similar in leaf development to broad-leaved angiosperms, and the "typical" monocot leaf development would then be a synapomorphy of a subgroup of the monocot clade, perhaps the entire group minus Acorales and Alismatales. But Scindapsus in Araceae , (but not Arisaema, Orontium, and Zamioculcas) and even Acorus (Acoraceae) itself, may develop in a "typical" monocot fashion (Troll & Meyer 1955; Bharathan 1996; Doyle 1998b). Although Acorus has a "typical" linear monocot leaf, many Araceae do not, and scattered through the monocots are taxa with petioles and net-veined leaf blades of a variety of morphologies; these include Smilax, Trillium (Liliales), Dioscorea (Dioscoreales), Lowia (Zingiberales - such leaves are very common here), Stemona (Pandanales), etc. Smilax has paired tendrils near the base of the petiole, and ligules, which may be paired and born either at the base (e.g. Potamogetonaceae) or top (e.g. Poaceae) of the petiole or sheath, are scattered through the group. Note, however, that such paired structures are never called stipules. Truly compound leaves are rare (Zamioculcas is an example), but cell death may result in the leaves appearing to be compound (Arecaceae, a few Araceae) or having distinctive perforations (some Araceae and Aponogetonaceae).

It is interesting that monosymmetric flowers in monocots are very frequently presented in the common angiosperm position with the median sepal adaxial; the main exceptions are most Zingiberales. It is unclear why this should be so (well, one can come up with stories, e.g., the abaxial tepal that acts as a landing platform is partly supported by the two adjacent tepals of the outermost perianth whorl [and in those Commelinaceae where the abaxial tepal is very small, perhaps the well developed inflorescence bract serves the same purpose], whereas if the landing platform were a member of the outer whorl, there would not be the same support...). Indeed, floral orientation as a whole in the monocots is quite variable, and in part depends on the presence and position of the prophyll/bracteole, and also on the existence of other structures on the pedicel (see e.g. Eichler 1875; Engler 1888; Remizova et al. 2006b). Stuetzel and Marx (2005) note the variability in the position of monocot bracteoles; they think that this may be because what appear to be axillary flowers in fact represent reduced racemes.

Monocots and "dicots" were often distinguished in the past by the 3-merous flowers of the former and the predominantly 5-merous flowers of the latter, even as it was realised that some of the "primitive dicots" might have more or less 3-merous flowers. With our current knowledge of phylogeny and floral development, it seems that a 3-merous perianth in particular is widespread and may even be a synapomorphy for a clade [[Chloranthaceae + magnoliids] [monocots [Ceratophyllaceae + eudicots]]] (Soltis et al. 2005b and literature cited). The two perianth whorls in monocots are similar and petaloid, being called tepals; however, there is usually a slight different between the members of the two whorls. The stamens are individually opposite members of the two whorls, indeed, even the outer whorl may not encircle the floral apex. All in all, the 3-merous flowers of the monocots are rather highly stereotyped, usually being pentacyclic: pentacyclic 3-merous flowers are at best extremely uncommon in broad-leaved angiosperms and are here considered to be an apomorphy for monocots (cf. Soltis et al. 2005b; Bateman et al. 2006b).

Note that how the anther wall develops in Acorus is unclear (Rudall & Furness 1997), although it inclines to the monocot "type" (Duvall 2001). Given the diversity of carpel development in monocots in, or near the base of, the basal pectinations in the monocot tree here - whether or not the basic condition for monocot carpels is to be free or somewhat connate is unclear (e.g. Chen et al. 2004; Remizowa et al 2006a). Remizowa et al. (2006b) summarize variation in gynoecial morphology in some of these monocots. Septal nectary morphology is rather variable and is difficult to categorise when the carpels are more or less free.

For monocots, in addition to references in the notes on the Characters page and under individual orders and families, there is much interesting information in Arber (1920, 1925), Dahlgren et al. (1985) and Tillich (1998); Tomlinson (1970) outlined their morphology and anatomy, emphasizing the woody groups. Volumes III and IV of Families and Genera of Vascular Plants, edited and with useful outline classications by Kubitzki (see especially 1998a, c), also contain a great deal of information. For the evolution of monocot seeds, see Danilova et al. (1990: somewhat outdated), for information on dimorphism in the cells of the root epidermis and hypodermis, see Kauff et al. (2000), for the distribution of operculate pollen, see Furness and Rudall (2006b), for the development of callose plugs in the pollen tube - quite often complete and regularly spaced in broad-leaved angiosperms, incomplete and irregularly spaced in monocots, see Mogami et al. (2006), for nuclear DNA content, see Bharathan et al. (1994), for seedling morphology, see Tillich (2007), for discussion on the evolution of the berry, see Rasmussen et al. (2006), and for antipodal cells, see Holloway and Friedman (2008a, b).

Phylogeny. Both molecular and morphological data strongly support the monophyly of monocots. However, monophylyy was not recovered in some morphological studies such as those by Hay and Mabberley (1991); Araceae were independently derived from broad-leaved angiosperms, perhaps from Nymphaeales. Similarly, in an analysis of fifteen chloroplast genomes, the five monocots included were not even always monophyletic... (Goremykin et al. 2005; see Duvall et al. 2006 for other studies in which monocots appear not to be monophyletic - the 18S gene is implicated in producing this topology).

The analysis of morphological characters alone in monocots tends to produce trees with little resolution and little support for those branches that are resolved (e.g. Li & Zhou 2006: support only for Alismatales minus Aracaeae and for Zingiberales). Relationships within monocots as outlined in molecular studies by Chase et al. (1995a, 1995b, 2000a, 2005), Tamura et al. (2004), Chase (2004), Janssen and Bremer (2004: rbcL only, but 878 genera from 77 families), Graham et al. (2006: to 16 kb chloroplast DNA/taxon examined), Givnish et al. (2006b), Chase et al. (2006), and Li and Zhou (2007) are followed here; further comments may be found at various nodes within the monocot tree. Acorus seems to be sister to all other monocots (see also Duvall et al. 1993a, b; Soltis et al. 2007a), a relationship recovered in most studies. Givnish et al. (2005: ndhF gene alone) found very much the set of relationships in the tree here, although Pandanales grouped with Liliales (low support) and Dasypogonaceae were sister to [Commelinales + Zingiberales].

Note, however, that Stevenson et al. (2000) suggest a rather different set of relationships - Acoraceae + most of Alismatales form a clade sister to all other monocots, Araceae a clade sister to the remainder. Davis et al. (2001) found a similar clade of Acoraceae + Alismatales (as delimited here) sister to other monocots. Davis et al. (2004) noted that this latter set of relationships was not found when rbcL sequences were analysed alone, but it appeared when mitochondrial atpA sequences were analysed, both alone and in the combined analysis (see Davis et al. 2006: four genes, two nuclear and two chloroplast, matK also supports this relationship). Characters of floral development also seem to be consistent with an Acoraceae-Alismatales relationship (e.g. see Buzgo 2001). Interestingly, a three-nucleotide deletion in the atpA gene is found in Acoraceae and Alismatales as recognised here, although neither in Cymodoceaceae nor Tofieldiaceae (Davis et al. 2004). Acoraceae show a substantially accelerated rare of molecular evolution in at least some mitochondrial genes (G. Petersen et al. 2006b), although they were nevertheless sister to remaining monocots in their combined trees. In another analysis of mitochondrial genes, again, with a much higher rate of change in Acoraceae and Alismatales, although not in Tofieldiaceae and Araceae (G. Petersen 2006c), Acoraceae linked with the fast-evolving group.

Indeed, G. Petersen et al. (2006b) found mitochondrial data in general to be rather incongruent with plastid data, for instance, Orchidaceae grouped with Dioscoreaceae and Thismia, and the positions of Liliales, Asparagales and Dasypogonaceae in particular were very labile. Although G. Petersen et al. (2006b) suggested that the incongruences "could equally well refute the phylogenies based on plastid data" (Petersen et al. 2006b: p. 59), this seems unlikely; problems caused by distinctive properties of the evolution of the mitochondrial genome seem more likely.

Previous Relationships. Lindley (1853) thought that the monocots that had leaves with reticulate venation, which he called the dictyogens, were intermediate between the exogens (dicots) and the endogens (other monocots). Indeed, some morphological cladistic studies have also placed net-veined monocots as sister to all other monocots, suggesting that this leaf venation was plesiomorphic in the monocots. This is largely because the broad-leaved angiosperm outgroups have similar features (Stevenson & Loconte 1995, see also Dahlgren et al. 1985; Yeo 1989; Li & Zhou 2006, etc.: Chase 2004). Cladistic analyses of the net-veined taxa by themselves (Conran 1989) also suggested relationships which now seem rather unsatisfactory.

ACORALES Reveal, see Main Tree, Synapomorphies.

Inflorescence a spadix [dense spike] with spathe; flowers weakly monosymmetric [abaxial member of outer T whorl precocious and large], tapetal cells 2-4-nucleate, tectum continuous, carpels ascidiate-plicate, syncarpy congenital, ovules straight; endosperm copious, perisperm [derived from nucellar epidermis] +, not starchy; collar rhizoids +. - 1 family, 1 genus, 2-4 species.

ACORACEAE Martinov   Back to Acorales

Vessels also in rhizomes, perforations long-scalariform, porose; stem with endodermis; leaves two-ranked, equitant and isobifacial [oriented edge on to the stem], sheath open; peduncle with two separate vascular systems; bracts and bracteoles 0 [but see below]; flowers rather weakly monosymmetric, T ± hooded, anther thecae confluent apically on dehiscence, endothecial thickenings stellate, pollen sulcus lacking ectexine, endexine lamellate, intra-ovarian trichomes +, placentae apical, pendulous, ovules several/carpel, integuments with hairs, hypostase massive, style broad, massive, stylar canal with exudate; fruit a berry, P persistent; n = 9, 11, 12; first leaf terete, unifacial.

1[list]/2-4. E. America to East and South East Asia (Map: from Hultén 1962; Fl. N. Am. 22: 2000, perhaps naturalised in Europe and America, see Mayo et al. 1997). [Photo - Habit.]

• Acoraceae are recognisable by their sweetly-smelling, two-ranked, isobifacial leaves and their densely spicate inflorescence overtopped by and appearing lateral to the leaf-like spathe. The flowers are small, perfect and pentacyclic.

Chemistry, Morphology, etc. The root stele is pentarch. The abaxial tepal is large, bract-like, and encloses the young flower; it looks as if it has "merged" with the bract (Buzgo 2001), being depicted as an organ of "hybrid" nature (Bateman et al. 2006b). There are non-secreting slits in the ovary septae; if these are considered to be septal nectaries, this feature becomes a synapomorphy (subsequently lost many, many times) of monocots as a whole. The ovules are encased in mucilage secreted by the intra-ovarian trichomes.

Some information is taken from Kaplan (1970a: leaf development), Tillich (1985: seedling), Grayum (1987: general), Carlquist and Schneider (1997: anatomy), Bogner and Mayo (1998: general), Buzgo and Endress (2000) and Buzgo (2001: both floral morphology), Keating (2003a: anatomy), Soukup et al. (2005: root development, intermediate) and Stockey (2006: evaluation of fossil remains). For a checklist and bibliography, see Govaerts and Frodin (2002) and World Checklist of Monocots.

Synonymy: Acoranae Reveal