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, xylem exarch; shoot apical meristem complex; arbuscular mycorrhizae +; stem with ectophloic eustele, endodermis 0, xylem endarch; 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 ?; leaf vascular bundles collateral; leaves spiral, simple, axillary buds?, prophylls [including bracteoles] two, lateral; plant heterosporous, sporangia eusporangiate, on sporophylls, sporophylls aggregated in indeterminate cones/strobili; true pollen [microspores] +, mono[ana]sulcate, pollen exine and intine homogeneous, ovules unitegmic, crassinucellate, megaspore tetrad tetrahedral, only one megaspore develops, megasporangium indehiscent; male gametophyte development endo/exosporic, gametes two, with cell walls; 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, 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, 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 sieve plate, companion cells from same mother cell that gave rise to the tube, the sieve tube with P-proteins; nodes unilacunar; stomata with ends of guard cells level with aperture, paracytic; leaves with petiole and lamina [the latter formed from the primordial leaf apex], development of venation acropetal, 2ndary veins pinnate, fine venation reticulate, vein endings free; flowers perfect, polysymmetric, parts spiral [esp. the A], free, numbers unstable, P not differentiated, outer members not enclosing the rest of the bud, A many, development centripetal, 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, pollen subspherical, binucleate at dispersal, trinucleate eventually, tectum continuous, endexine compact, lamellate only in the apertural regions, pollen tube elongated, with callose plugs, penetrating between cells, growth rate moderate, siphonogamy occuring, nectary 0, G free, several, ascidiate, with postgenital occlusion by secretion, few [?1] ovules/carpel, ovules marginal, anatropous, bitegmic, micropyle endostomal, integuments 2-3 cells thick, megasporocyte single, megaspore lacking sporopollenin and cuticle, chalazal, female gametophyte ?type, stylulus short, stigma ± decurrent, wet [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; 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/PHYC 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. Furthermore, 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; pollen tectate-columellate, tectum reticulate [perforated]; nucleus of egg cell sister to one of the polar nuclei; ?genome duplication; "DEAER" motif in AP3 and PI genes lost, gaps in these genes.

ALISMATALES + PETROSAVIALES [[DIOSCOREALES + PANDANALES] [LILIALES [ASPARAGALES + COMMELINIDS]]]: ethereal oils 0; raphides +, druses 0; leaf ptyxis variants of supervolute-curved; endothecium develops directly from undivided outer secondary parietal cells, endexine 0, carpels plicate, (septal [epithelial] nectaries +); endosperm nuclear/helobial.  Back to Main Tree

ALISMATALES Dumortier  Main Tree, Synapomorphies.

Plant rhizomatous; mycorrhizae absent; starch grains pteridophyte-type, amylophilic; A extrorse, tapetum amoeboid, cells uninucleate, carpels with completely unfused canals, styles +, stigma dry [common]; endosperm helobial; embryo large, (chlorophyllous); seedling with hypocotyl and root well developed. - 14 families, 166 genera, 4490 species.

Stem-group Alismatales are dated to ca 131 million years before present, crown group Alismatales to ca 128 million years before present (Janssen & Bremer 2004; ca 133 and 103 million years before present respectively in Bremer 2000b); the oldest fossils assignable to this clade are recently discovered and from the Early Cretaceous, 110-120 my old (Araceae-Pothoideae-Monstereae: Friis et al. 2004, see Stockey 2006 for a review of the fossils that have been placed in Alismatales). Alismatales include the only marine angiosperms. Les et al. (2003) discuss the distributions of a number of the hydrophytic taxa of this clade; most of them are rather young. The apparent absence of mycorrhizae in this group may be connected with the prevalence of the aquatic habitat its members prefer; mycorrhizae are usually absent in such situations. Caterpillars of Pyralidae-Schoenobiinae are found on aquatic monocots, as are larvae of Chrysomelidae-Donaciinae (Powell et al. 1999; Jolivet 1988); the latter, at least, are found on aquatic plants in general.

The group includes a number of small families, partly because the adaptations associated with the aquatic habitat are so striking that the flowers and inflorescences in particular of these families are very different from one another. Cox and Humphries (1993) and Les et al. (1997) and references therein discuss the pollination devices of water-pollinated Alismatales, both marine and freshwater. Chen et al. (2004b) discuss the evolution of various life forms in the group - parallelisms are common. Sulphated phenolic compounds are common in seagrasses, including members of Hydrocharitaceae (McMillan et al. 1980), and also probably arose in parallel; their function is unclear, although they are probably involved in adaptation to life in the marine habitat.

The root stele is often tri- to pentarch. When leaves are petiolate, bundles are in an arc; inverted bundles are also common. In some Alismatales there appears to be a merger between the bracte subtending the flower and the abaxial tepal (Buzgo 2001). There have been suggestions that flowers in Alismatales are really pseudanthial (Soltis et al. 2005 for references). Is the pollen endexine ever lamellate (it is in Acorus)?

Tofieldiaceae were placed here with only moderate support (Källersjö et al. 1998; Chase et al. 2000a; Graham et al. 2006 - sister to the rest of the order, but limited sampling); they are rather different from other Alismatales, as can be seen by their numerous potential apomorphies. However, Tamura et al. (2004), Janssen and Bremer (2004) and Givnish et al. (2006b), and Chase et al. (2006: strong support) all place Araceae sister to rest of the order, and Tofieldiaceae then sister to the remaining taxa; this is the topology followed here. For relationships within the core Alismatales, see Les et al. (1997 - on which the rest of the tree is largely based), also Kato et al. (2003), Chen et al. (2004b) and G. Petersen et al. (2006c: 2 mitchondrial and 1 chloroplast genes); a number of uncertainties over relationships remain and G. Petersen et al. (2006c) do not even recover a monophyletic Hydrocharitaceae + Alismataceae s.l. + Butomaceae. The tree in Janssen and Bremer (2004: see above) is largely similar to that below, but the positions of Aponogetonaceae and Scheuchzeriaceae are reversed, and Ruppiaceae are placed sister to Zosteraceae + Potamogetonaceae. For a possible [Acorus + Alismatales] relationsip, see the former.

Riley and Stockey (2004) describe the venation of a number of net-veined members of this order in considerable detail; such leaves usually have tertiary veins. It has been said that Alismatales, inc. Araceae, are the only monocots in which green (chlorophyllous) embryos have been reported (Seubert 1993), although they are also known from some Amaryllidaceae-Amaryllidae.

For seedling morphology, see Tillich (1985), for information on pollen, see Grayum (1992), for that on ovules, see Igersheim et al. (2001), and for carpel evolution, see Chen et al. (2004a); Den Hartog (1970) gives a comprehensive taxonomic account of the marine Alismatales.

Includes Alismataceae, Aponogetonaceae, Araceae, Butomaceae, Cymodoceaceae, Hydrocharitaceae, Juncaginaceae, Limnocharitaceae, Posidoniaceae, Ruppiaceae, Potamogetonaceae, Scheuchzeriaceae, Tofieldiaceae, Zosteraceae.

Synonymy: Alismatales Dumortier, Aponogetonales Hutchinson, Arales Dumortier, Butomales Hutchinson, Cymodoceales Nakai, Elodeales Nakai, Hydrocharitales Dumortier, Juncaginales Hutchinson, Najadales Dumortier, Posidoniales Nakai, Potamogetonales Dumortier, Ruppiales Nakai, Scheuchzeriales B. Boivin, Tofieldiales Reveal & Zomlefer, Vallisneriales Nakai, Zosterales Nakai - Alismatanae Takhtajan, Aranae Reveal, Butomanae Reveal, Najadanae Reveal, Zosteranae Doweld - Alismatidae Takhtajan, Aridae Takhtajan - Aropsida Bartling, Hydrocharitopsida Bartling, Najadiopsida Hoffmannsegg & Link

ARACEAE Jussieu, nom. cons.   Back to Alismatales

(Stem tuberous, or erect/climbing); cyanogenic glucoside triglochinin, flavone C-glycosides +; dimorphic root hypodermis +; sieve tube plastids also with starch; pseudopetiole bundles scattered; stomata unorientated, also anomo- ["basal" genera] and tetracytic; leaves usu. with pseudopetiole, lamina and (pseudo)midrib, tertiary venation cross to reticulate, base with lateral (auriculate) flanges, (ligule +); inflorescence scapose, spathe and spadix [dense spike] +, bracts 0; flowers 2-3-merous, in latter case P with median member of outer whorl adaxial, T with single trace, free (connate), (microsporogenesis simultaneous; pollen often starchy), ektexine +, septal nectaries 0, carpels (basally) ascidiate, fusion usu. congenital, loculus usu. with secretion, ovules tenuinucellate, outer integument 8-26 cells across [in basal pectinations], nucellar cap +, style at most short, stigma also wet; fruit a berry; testa multiplicative, often parenchymatous, or with exotesta and/or endotesta and mesotesta lignified; cotyledon not photosynthetic (collar rhizoids or collar roots +), cataphylls initially developed.

106[list]/4025 - 7 subfamilies below. Mostly tropical.

Gymnostachydoideae + Orontioideae: ovules straight [atropous].

See Buzgo (2001) for discussion on the gyneocial construction of this clade; the gynoecium often has but a single loculus.

1. Gymnostachydoideae Bogner & Nicolson

Vascular bundles with fiber sheaths and girders; stomata parallel; leaves 2-ranked, not petiolate, linear, venation parallel, margins minutely toothed; inflorescence complex, branched, spathe 0; flowers 2-merous, A thecae forming tip above slit, G 1, ascidiate, loculus ?lacking secretion, 1 apical unitegmic ovule/carpel, micropyle 0, stigma dry; testa 0; endosperm copious, green, with starch, embryo green; n = 12; collar rhizoids 0.

1/1: Gymnostachys anceps. E. Australia (Map: from Mayo et al. 1997).

There is no micropyle. The leaf bundle anatomy is distinctive (Keating 2002).

2. Orontioideae Mayo, Bogner & Boyce

Flavonols +, glycoflavones 0; (collenchyma in cortical bands), bundle-associated fibre strands +/0; (laticifers + - Orontium); sieve tube plastids with no starch; leaves spiral, elliptic; (spathe 0); flowers 2-3-merous, G inferior (not - Orontium), 1-2 ± basal (hemianatropous - Orontium) crassinucellate [?: Symplocarpus] ovules/carpel; endosperm ± 0; n = 13-15.

3/6. Temperate East Asia, W. and E. North America (Map: from Mayo et al. 1997).

Buzgo (2001) suggests that Orontium is more like core Araceae than is Lysichiton or Symplocarpus. Orontieae and Symplocarpeae are anatomically distinct (Keating 2003a), and the former also have a long internode (not always obvious) between the base of the spike and the subtending leaf or spathe. The "cataphylls" of this group are relatively long, linear structures (Tillich 2003).

Synonymy: Orontiaceae Bartling

Lemnoideae + Pothoideae + Lasioideae + Calloideae + Aroideae: ?

3. Lemnoideae Engler

Thallus-like, stemless, floating aquatic herbs, (roots 0); collenchyma and bundle fibers 0; vessels 0; P 0, A 1, monothecal, or 2, pollen ulcerate, spiny, G 1, 1(atropous)-7 ovules/carpel, micropyle endostomal, embryo sac Allium-type, stigma funneliform; fruit an achene [sort of]; seed operculate; endosperm cellular, starchy, embryo undifferentiated; n = 10, extensive polyploidy and dysploidy; hypocotyl and primary root 0, cotyledonary sheath broad and photosynthetic.

5/37. World-wide (Map: Hultén 1962; Meusel et al. 1965; Landolt 1986 -"absence" in tropical America and Africa may be due to undercollecting). [Photo - Wolffia]

The vegetative body is variously interpreted as being some combination of leaf and shoot, while the reproductive parts either represent a reduced but perfect flower or a very highly reduced inflorescence. Wolffia and Wolffiella lack both roots and veins in the thallus, and the thallus of the former may be less than 2.5 mm across. Whether or not the endosperm is really cellular must be confirmed.

Although the early Tertiary fossil Limnobiophyllum seems "intermediate" between Lemnoideae and Pistia (Aroideae) (Stockey et al. 1997), those two groups are not at all close in molecular phylogenies.

For a general bibliography, see Landolt (1980), cytology, Urbanska-Worytkiewicz (1980), morphological details, see Landolt (1986, 1998), chemistry, etc., see Landolt and Kandeler (1987), for phylogeny in particular see Les et al. (2002) and Rothwell et al. (2004), and for speciation, see Crawford et al. (2006).

Synonymy: Lemnaceae Martynov, nom. cons., Woffiaceae Bubani

Pothoideae + Lasioideae + Calloideae + Aroideae: petiole clearly differentiated from sheathing base.

4. Pothoideae Engler

Stem usu. aerial; (separate stem cortical vascular system +); (vessels in stem); H- or T-shaped trichosclereids + (0), styloids +; leaves 2-ranked or spiral, elliptical to complex, higher-order venation reticulate, pseudopetiole apically geniculate; crystals often surrounding the embryo.

16/1260. Tropical, few in Africa (Map: from Mayo et al. 1997).

Climbers and epiphytes are notably common in this clade, particularly in Potheae.

See Tam et al. (2004) for what is known about relationships within this clade.

4a. Potheae Engler

Fibers ensheathing bundles; flowers 2-3-merous; anther thecae often forming tip above slit, pollen forate (Anthurium), 1-2 basal/parietal apotropous ovules/carpel; spathe persistent in fruit; endosperm with starch, 0 (copious - Anthurium), (embryo green); n = (10) 12 (14-15); (seedling internodes long; very short unifacial part of cotyledon, cataphylls 0 - Anthurium).

4/900: Anthurium (825, notably variable in leaf morphology), Pothos (70). Tropical America, Madagascar to South and Southeast Asia, Malesia and N.E. Australia. [Photo - Flowers, Fruits.]

Pothos and relatives have monopodial shoots, distichous leaves, and flattened petioles; they are mostly climbers.

Note that although Keating (2000b) records collenchyma for a few members of this clade, for some of the same taxa, Gonçalves et al. (2004) fail to find it. The ovules of Pothos macrophyllus are shown by Buzgo (2001) as being anatropous and apotropous, although Pothos is described in the same paper as having straight [atropous] ovules. The inner integument of Pothos is ca 6 cells across.

Synonymy: Pothaceae Rafinesque

4b. Monstereae Schott

Fibers ensheathing or capping bundles; (laticifers +); flowers 2(-3 - Spathiphylleae)-merous, P often 0, pollen inaperturate, extended monosulcate or zonate, 1-4(-many) often basal (hemianatropous) ovules/carpel; spathe soon deciduous; endosperm + [Spathiphylleae] or 0; n = 12, 14, 15, 21 [much polyploidy, n = 30 common].

12/360: Rhaphidophora (100: paraphyletic), Rhodospatha (75). Tropical South and Southeast Asia to the Pacific, South America (Africa).

For fenestration in Monstera, see Melville and Wrigley (1969). It is possible that the presence of ?protective trichosclereids in the stylar tissue is correlated with the deciduous nature of the spathe.

Lasioideae + Calloideae + Aroideae: ?

5. Lasioideae Engler

Tuberous or rhizomatous, terrestrial or rooted aquatics; laticifers +; sieve tube plastids with little starch; fibers ensheathing or capping bundles; leaves ?spiral, pseudopetiole long, warty, aculeate, or strikingly coloured, ± geniculate apically; inflorescence flowering basipetally; pollen sulcus with ectexine lamella and thick bilayered endexine [outer: flakes or lamellae; inner: spongy], G 1 [2-3], 1-2(-many - esp. Cyrtosperma) variously arranged apotropous (campylotropous) ovules/loculus; endosperm thin (0), embryo green, curved; n = 13.

10/58. India and Southeast Asia to the Pacific (Africa - Lasimorpha) (Map: from Mayo et al. 1997).

Note that although Keating (2000b) records collenchyma for a few members of this clade, for some of the same taxa, Gonçalves et al. (2004) again fail to find it. See Hesse (2002) for pollen morphology; the sulcus is unique among angiosperms.

Synonymy: Dracontiaceae Salisbury

Calloideae + Aroideae: ?

6. Calloideae Endlicher

Rooted aquatic; laticifers +; vascular bundles amphivasal; leaves 2-ranked, elliptic, sheath long, ligulate; P 0, pollen biporate, G 1, with 6-9 basal crassinucellate ovules; endosperm +, embryo green; n = 18 (27); seedling roots green.

1/1: Calla palustris. Circumboreal (Map: from Mayo et al. 1997).

Synonymy: Callaceae Bartling

7. Aroideae

Plants monoecious (dioecious); spathe differentiated into tube plus blade.

7a. Zamioculcadeae Engler

Leaves compound, petiole geniculate; staminate flowers: A (connate), introrse to extrorse, pollen zonasulcate, columellae winding, forming a sort of internal tectum as well as the external tectum, endexine lamellate, intine thin, pistillode +; carpellate flowers: G [2], axile, one ascending ovule/carpel; seeds almost lacking endosperm; n = 17.

2/6. Africa, Kenya to Natal.

In floral morphology Stylochaeton goes here, but it has the same pollen as the bulk of Aroideae and it has simple leaves. Bogner and Hesse (2005) raised the group [Zamioculcas + Gonatopus] to subfamilial status (Zamioculcadoideae Bogner and Hesse), but the position of Stylochaeton (pollen reticulate, but ektexine reduced) needs to be clarified; it is likely to affect the synapomorphies of whatever clade to which it is assigned. Furthermore, if Calloideae are sister to Aroideae, the position of perianth loss and laticifer gain on the tree may become problematic, and, finally, note that the pollen of Lasioideae, at least, has a lamellated endexine rather like that of Zamioculcadeae.

7b. The Rest.

Habit various; (anastomosing) laticifers +; collenchyma in cortical bands or bundle-associated strands (0); fibers associated with bundles various; (biforine raphides [wall thick, except for papillae at the two ends, lignified, cell contents mucilaginous] +); leaves spiral, very variable, (vein endings free); plants monoecious (dioecious); P 0 (Stylochaeton +, connate), A connate (not - Philodendron), connectives thick, pollen inaperturate, (spiny), ektexine thin, often lacking sporopollenin, endexine thick, spongy, intine massive, (G 1, several [2-4], placentation parietal, apical, basal); endosperm +/0 (with starch; storage cotyledons; embryo green); n = 7+ [esp. variable in Cryptocoryne], 13, 14, 17 common; (cotyledon sheath photosynthetic, bifacial [e.g. Colocasia, Philodendron, Xanthosoma], even leafy; collar rhizoids +).

68/2665: Philodendron (500: for a phylogeny, see Gauthier et al. 2008 - Homalomena may be part of this clade), Arisaema (170), Amorphophallus (150), Homalomena (140), Schismatoglottis (120), Alocasia (70), Xanthosoma (60), Cryptocoryne (50). Tropical and warm temperate (the latter - Arum and relatives) (Map: from Mayo et al. 1997). [Photo - Flowers.]

Zamioculcas, Gonatopus, Stylochaeton have a perianth; Zamioculcas has introse anthers. For a discussion on the evolution of the distinctive pollen that characterises most Aroideae, see Hesse (2006b). Pistia has exostomal ovules, and in a number of taxa the ovules are tenuinucellate, in others straight [atropous], the micropyle bistomal, a nucellar cap and integumentary endothelium present, and so on. The sterile flowers that are often found between the staminate and carpellate zones of the inflorescence develop in a variety of ways, but whether this implies that there are different pathways in the evolution of imperfect flowers in Aroideae ia unclear (cf. Barabé et al. 2004).

Synonymy: Arisaraceae Rafinesque, Caladiaceae Salisbury, Pistiaceae C. Agardh

• Araceae are herbs with leaves that are usually divided into a petiole and expanded blade. They have a distinctive inflorescence of a more or less petaloid spathe plus a spadix made up of densely-packed, sessile, ebracteate flowers - in many taxa the spadix has a large, terminal, sterile part. The fruit is a berry.

Distinctive pollen that can be assigned to Pothooideae-Monstereae has been found in Early Cretaceous deposits of the late Barremian-early Aptian of some 110-120 my old in Portugal (Friis et al. 2004); other pollen types that may also be Araceae were found at the same place (see also Hesse & Zetter 2007). The site is now, alas, developed. Stem-group Araceae have been dated to ca 131 million years before present, crown group Araceae to ca 128 million years before present (Janssen & Bremer 2004). Araceae are not much liked by butterfly caterpillars (Ehrlich & Raven 1964). A number of species of galerucine beetles (Aplosonyx) have been found feeding on laticiferous Aroideae from South East Asia where they make circular tranches in the leaves to interrup the latex flow and then eat out the portion of the leaf so isolated - it looks as if there are paper punch holes in the blade (Darling 2007); galerucines are known from other monocots and beetle herbivory in Araceae may be geographically more widespread. Many Araceae are plants of shaded conditions, and net veined leaves and fleshy fruits are associated with this habitat in monocots (Givnish et al. 2005).

Thermogenesis has been detected in the flowers of a number of Araceae, and this is produced both by uncoupling proteins and the mediation of an alternative oxidase (Watling et al. 2006; Onda et al. 2008 and references). A nectar-like exudate is sometimes produced by stigmatic hairs, etc., as in Anthurium (Daumann 1931).

Raphides in those taxa that have been studied are twinned crystals, H-shaped in transverse section, and often with lateral barbs (Sakai & Hanson 1974); Lemna, etc., also have such raphides. Gonçalves et al. (2004) note that some taxa with perfect flowers may have collenchyma at the apex or base of the petiole; their comparative data is of collenchyma presence at the middle of the petiole. This may perhaps explain the apparent conflict in the literature (cf. Keating e.g. 2000b). A number of taxa have fenestrate leaves, while the leaves of climbers are often strongly heteroblastic. In addition to Gymnostachys, I have seen one taxon (unnamed, from Thailand) with softly dentate/spinulate leaves. When flowers are 2-merous, the outer pair of tepals are lateral. The pollen is quite often extruded in threads, but I do not know the distribution of this feature. Some taxa have binucleate tapetal cells (Wunderlich 1954). Pseudomonomery has been documented for the family (Eckardt 1937; see Buzgo 2001). The megaspore that germinates is often micropylar in other than Aroideae and Calloideae, where it is chalazal, although not in e.g. Lysichiton (Grayum 1991). The uninucleate chalazal haustorium of Arum maculatum is reported to be 24,576 n (Werker 1997). Johri et al. (1992) describe the endosperm as being cellular, but it can be interpreted as being helobial. Variation in seedling morphology is extreme (Tillich 1985).

Early hypotheses of phylogeny based on restriction site analysis (French et al. 1995) suggested rather pectinate relationships in the family, but a consensus tree of morphological characters (Mayo et al. 1997) and a more recent tree based on the analysis of five plastid genes (Mayo et al. 2003) show somewhat less resolution. However, the clade (Gymostachydoideae + Orontioideae) remains as sister to all the rest of the family, and Lemnoideae are strongly supported as sister to the remainder; the groupings are largely those also evident in French et al. (1995). Barabé et al. (2004) found the Calla was embedded in Aroideae, although without any strong support; Lasioideae were not clearly separated from Aroideae, but again the support was weak (below 50% bootstrap in both cases). Although a recent trnL-trnF phylogeny (Rothwell et al. 2004) placed Callopsis and Asterostigma (both Aroideae) outside a clade with 100% jackknife support that included other Aroideae, Lemnoideae and Pothooideae, Tam et al. (2004: trnL-F sequences, Calla not examined) again suggest the phylogeny is rather pectinate. The topology they present, quite well supported, is that given here; Zamioculcas is sister to other Aroideae examined. Gonçalves et al. (2007) discuss the phylogeny of the Andean Spathicarpeae, a clade in which the spathe is adnate to the spadix, many of which grow in very dry and/or high conditions.

I am grateful to Monica Carlsen and Richard Keating for discussions on Araceae (the latter [Keating 2003a, 2004a] divides Aroideae into three subfamilies) and to Simon Mayo for comments. Much information is taken from Mayo et al. (1997, 1998); see also Gatin (1921: seedlings, unfortunately Gatin died before he could make more than this "première contribution"), Ertl (1932: venation and petiole anatomy, a more normal monocot venation may be common in the basal subfamilial pectinations), Ray (1988: shoot organisation), Tillich (1985, 2003b: seedlings), Grayum (1991, 1992: pollen morphology, much variation in surface, etc.), Seubert (1993: starch grains, seeds and seedlings, very variable), Dring et al. (1995: chemistry), Behnke (1995a: sieve tube plastids), French (1998: stem anatomy, extremely variable), Buzgo and Endress (1999: Gymnostachys), Weber et al. (1999: pollen), Bown (2000: general), Keating (2000b: collenchyma, 2003a: general anatomy, b: leaf anatomy, 2004 a: classification, b: raphides), Gonçalves et al. (2004: collenchyma), Jayalakshmi (2004: pollen variation, phylogenetic framework inadequate), Hesse (2006a, b: summary of pollen variation, phylogenetic framework reasonable), Bogner and Petersen (2007: chromosome numbers) and Barabé and Lacroix (2008: development of Anthurium). For a checklist and bibliography, see Govaerts and Frodin (2002) and the World Checklist of Monocots.

Tofieldiaceae + [Hydrocharitaceae + Scheuchzeriaceae groups]: carpels free.

TOFIELDIACEAE Takhtajan   Back to Alismatales

Steroidal saponins, chelidonic acid +; vessels?; fibers mixed with phloem; sieve tube plastids also with polygonal crystals; stomata anomocytic; also prismatic crystals +; leaves 2-ranked, equitant, isobifacial; inflorescence a raceme, bracteate (flower single - Harperocallis), calyculus below individual flowers (some Tofieldia 0); T free (basally connate), with one trace [Tofieldia], median member of outer whorl adaxial [Tofieldia], A (9-12 - Pleea; adnate to base of P; basally connate), introrse to latrorse, tapetum glandular, microsporogenesis simultaneous, pollen di(trichotomo)sulcate, septal or tepal nectaries +, carpels mostly plicate, periphery completely postgenitally fused, (placentation parietal), 5-many unitegmic ana-campylotropous ovules/carpel, thinly crassinucellate, integumentary obturator +, (long chalazal extension +), (style + - Isidrogalvia); fruit a septicidal capsule or follicle ["ventricidal"], (P persistent); seeds obliquely stacked, with appendages, phlobaphene +, tegmen thin; n = (14) 15 (16), chromosomes 0.9-2.5 µm long; radicle 0?, collar rhizoids + [Harperocallis].

3-5[list]/27. S.E. U.S.A., N.W. South America, N. temperate (Map: see Hultèn 1961; Meusel et al. 1965; Hultén & Fries 1986; Fl. N. Am. 26: 2002). [Photo - Flowers] [Photo - Flowers]

• Tofieldiaceae can be recognised by their equitant, isobifacial leaves; racemose inflorescences in which there is usually a 1-3-membered "calyculus" below the flower; and undistinguished monocot flowers with the tepals usually free and the tips of the carpels each with a clearly separate stylodium. The fruit is usually a septicidal capsule.

Stem-group Tofieldiaceae are dated to ca 124 million years before present, crown group Tofieldiaceae to ca 100 million years before present (Janssen & Bremer 2004: note their topology).

Branching in Tofieldiaceae needs study; Remizowa et al. (2005) suggest that the first two leaves of axillary shoots in Tofieldia (the adaxial prophyll and also the next leaf) are adaxial. Generalised comparisons between the calyculus of Tofieldiaceae, made up of two or three connate scales, with the spathe of Hydrocharitaceae and pseudodowhorls of bracts in Alismataceae have been made (Remizowa and Sokoloff 2003; Remizowa et al. 2006b). The nectaries of Tofieldiaceae may be unique to the group (Remizowa et al. 2006a for references).

Tofieldiaceae have often been included in other families, thus Dahgren et al. (1985) placed them - along with representatives of Nartheciaceae and Petrosaviaceae - in Melianthaceae, they were included in Melanthiales by Takhtajan (1997), and Tamura (1998) placed them in Petrosaviaceae (along with Nartheciaceae).

For Harperocallis, described from Florida in 1968, see McDaniel (1968), for general information, see Ambrose (1975, 1980), Zomlefer (1997b) and Tamura (1998 - as Nartheciaceae), for ovary, see Sterling (1979), for inflorescence and floral morphology, see Remizowa and Sokoloff (2003) and Remizowa et al. (2006a, b), and for sieve tube plastid type, see Behnke (2000, 2003); for a checklist of the family, see World Checklist of Monocots.

Hydrocharitaceae + Scheuchzeriaceae groups: plant aquatic (with floating stems), leaves emergent; stem with lacunae; little oxalate accumulation; raphides and druses 0 (prismatic crystals +); hairs 0; bulliform cells 0 [?this level]; pollen grains trinucleate; carpel fusion partial at the periphery; endosperm 0; seedling collar and collar rhizoids +.

The divergence of these two clades is ca 107 million years before present (Janssen & Bremer 2004).

Hydrocharitaceae produce only precocious axillary buds along their stems (Wilder 1975); resting buds are produced sporadically throughout this group. Non-medullated roots are quite common, occuring in e.g. Butomaceae, Alismataceae, Limnocharitaceae (Stant 1964, 1967), Aponogeton, Triglochin, Potamogeton, although roots of e.g. Posidonia are medullated (von Guttenberg 1968). There are a number of reports of sex chromosomes, e.g. in Phyllospadix (Harada 1956). At least some mitochondrial genes show an accelerated rate of change in these aquatic Alismatales (G. Petersen et al. 2006).

Much general information is taken from Tomlinson (1982); see Zindler-Frank (1976) for oxalate accumulation. There have been extensive cytological studies in the group, see e.g. Harada (1956), Uchiyama (1989), Sharma and Chatterjee (1967), and Costa and Forni-Martins (2003). Wilder (1975) discussed vegetative branching, inflorescence morphology, etc., in this group, members of which which he considered to be closely related.

[Hydrocharitaceae + Butomaceae] [Alismataceae + Limnocharitaceae]: apical meristems of vegetative axes bifurcating; C-glycosyl flavones +; inflorescence scapose, determinate, bracteate; P = K + C, both whorls with many traces, (stamen pairs +), carpels plicate; seeds exotestal; chromosomes (0.8-)2-13.6 µm long.

The prophylls of Limnocharis and Vallisneria may not be in the normal adaxial position (Wilder 1975).

For floral development, see Posluszny et al. (2000), for tepal vasculature, see Glück (1919).

Hydrocharitaceae + Butomaceae: ?

The divergence of these two clades is ca 88 million years before present (Janssen & Bremer 2004).

Butomaceae are embedded in Hydrocharitaceae in a rbcL analysis of Kato et al. (2003).

HYDROCHARITACEAE Jussieu, nom. cons.   Back to Alismatales

Branching?; flavone and phenolic sulphates +; vessels 0; endodermis obscure or thick-walled; (prophyll lateral); leaf base sheathing [?type] or not; inflorescence subtended by 2 often connate bracts; (A introrse), pollen inaperturate, spinulate, trinucleate, nectaries 3, staminodial (0), G inferior, also basally ascidiate [Stratiotes, Limnobium], closure by secretion only, loculi filled with secretion, placentae parietal, laminar, or subbasal, 1-many ovules/carpel, outer integument often 3< cells across, micropyle bitegmic, style single, short, stigmas usu. divided; fruit often ± fleshy; stone cells in mesotesta and endotesta (all testal cells ± thickened except the outermost wall), endotegmen with tuberculate inner wall alone persisting; n = notably variable, chromosomes (0.8-)2-10 µm long; cotyledon bifacial; extensive loss of mitochondrial genes.

18[list]/116 - four groups below. World-wide (Map: see Hultèn 1961; Hultén & Fries 1986; Fl. N. Am. 22: 2000; FloraBase 2005 - incomplete: van Steenis & van Balgooy 1966; den Hartog 1970 for marine taxa).

1. Hydrocharitoideae Eaton

Leaves involute or convolute, broad, margins entire, vascular bundles inverted, pseudopetiole +, ligules basal, adaxial or paired lateral [totally enclosing young leaves]; plants monoecious; staminate flowers: K 3, C 3, A 1-6; carpellate flowers: K 3, C (0) 3, G [3-9], placentae strongly intruded; exotestal cells much enlarged, exotegmic tuberculae +; n = 7-11, 13-15.

2/5. Temperate and subtropical. Also Limnobium.

Stratiotoideae [Anacharidoideae + Hydrilloideae]: roots unbranched; (ovules straight [atropous]).

2. Stratiotoideae Luersson

Leaves tristichous, in rosettes, spiny; plant dioecious, K 3, C 3; staminate flowers: A many, adaxial 5-17 fertile; carpellate flowers: staminodes +; n = 10+.

1/1: Stratiotes aloides. Eurasian.

The plant sinks to the bottom of the water in winter, rising to the surface in the summer.

Synonymy: Stratiotaceae

Anacharidoideae + Hydrilloideae: leaves submerged.

3. Anacharidoideae Thomé

Root trichoblasts 0 [Blyxa]; leaves whorled to spiral [usually opposite when scales], narrow, margins entire to spiny, pseudopetiole 0, (lamina broad, pseudopetiole +; fine veins reticulate - Ottelia); inflorescences axillary; plant dioecious (flowers perfect - Apalanthe, also Ottelia - petals large, A to 15); staminate flowers: released, usually as buds, P 3 + 3 (3), A 3 (+ 3 staminodes) or 6, (pollen with discontinuous exine, little or no sculpturing); carpellate flowers: hypanthium +, usu. long, P 3 + 3, staminodes +, G [3(-20+)]; fruit a capsule, indehiscent or irregularly dehiscent; seeds usually <30; n = ?6, 8, 9, 11, 12, 14, etc.

7/38. Tropical to temperate, esp. America.[Photo - Habit © D. Woodland, Blyxa Habit, Flower © M. Clayton.] and Egeria.

Pollination in those taxa where the staminate flowers are released may be epi- or hypohydrophilous. Blyxa has secondary pollen presentation and notably short chromosomes (Uchiyama 1989).

Synonymy: Blyxaceae (Ascherson & Gürke) Nakai, Elodeaceae Dumortier, Otteliaceae Chatin

4. Hydrilloideae Luersson

(Marine); root trichoblasts 0 [Vallisneria]; leaves (spiro)2-ranked or whorled, narrow, margins entire or toothed, pseudopetiole 0, (lamina broad, pseudopetiole + - Halophila); inflorescences axillary; perianth biseriate, undifferentiated, uniseriate, (0); staminate flowers: (released as buds), A 1-3, (1 staminode); carpellate flowers: hypanthium +, staminodes (2-)3, G [2-9]; fruit fleshy, capsular, or dehiscing irregularly; (exotegmic tuberculae +); n = 6-8, 10, 12, 15.

8/61: Naias (40). Tropical and subtropical, especially Old World; Naias subcosmopolitan. [Photo - Hydrilla, © H. Wilson], [Photo - Halophila, Enhalus, flower, © from D. Les website], Thalassia, fruit, © from D. Les website.]

For a phylogeny of Valisneria, see Les et al. (2008).

The leaves of Naias have an "auricle" at very base. Its staminate flowers have two envelopes and a single stamen. The carpellate flowers have a single envelope and a single ascidiate carpel with one basal ovule, the style is 1- or 2-branched. The fruit is an ?achene, sometimes with an exotegmen, the endosperm is nuclear, the embryo green; the cotyledon is unifacial. Najas has a well-developed root system, the roots being unbranched, but with many root hairs. Variation in chromosome length (1.6-11.7 µm) is considerable. For suggestions that the ovary, apparently superior, might really be inferior, see Miki (1937).

Synonymy: Enhalaceae Nakai, Halophilaceae J. Agardh, Hydrillaceae Prantl, Najadaceae Jussieu, nom. cons., Thalassiaceae Nakai, Vallisneriaceae Link

• Hydrocharitaceae are aquatic plants with petiolate or (usually) undifferentiated leaves. The inflorescence often has two fused (sometimes free) bracts at the base and the ovary is inferior, often with laminar or more or less strongly intruded parietal placentation, and the stigma lobes are bifid.

Stem group Hydrocharitaceae are dated to ca 88 million years before present, crown group Hydrocharitaceae to ca 75 million years before present (Janssen & Bremer 2004). Hydrocharitaceae such as Hydrilla and Egeria have C₄ photosynthesis with the metabolic compartmentalisation needed occuring within single cells (Bowes et al. 2002 for references). There is a great diversity of morphological variation, and the marine taxa are rhizomatous, with leaf-bearing short shoots; the plants may be tanniniferous. There is also a diversity of pollination mechanisms, entomophily, anemophily, epi- and hypohydrophily, selfing, hence the eleven family names available for the eighteen genera. Hypohydrophily has evolved at least twice (e.g. Naias, marine genera), and staminate flowers that detach and rise to the surface perhaps five times (Les et al. 2006 and references). In a number of cases the hypanthium elongates greatly, and the opening of the carpellate flower is on the surface of the water. Small detached staminate flowers borne above the surface of the water on reflexed sepals are caught by the carpellate flowers; these flowers may have two stamens (Nechamandra), three stamens and three erect staminodes that act as little sails (Lagarosiphon), or six stamens (Appertiella). Hydrilla is wind pollinated, the pollen being released explosively by the anthers, the anthers reaching the surface in little gas bubbles produced by the staminate flower, while in Elodea the pollen floats. In other taxa the hypanthium does not elongate, the carpellate flowers having long pedicels, again, detached staminate flowers are caught by the carpellate flowers, as in Maidenia and the marine Enhalus; in the former genus, there is a maximum of a mere 24 pollen grains per staminate flower. In the marine Halophila the pollen is released in chains, and pollination is under the water (Cook 1982, 1996).

Tanaka et al. (1997) suggest a series of quite well-supported nodes based on analysis of variation in two genes, the ultimate groupings recognised there are similar to those of Les et al. (1997). Najas is moderately associated with Hydrilla + Vallisneria, Enhalus with Halophila + Thalassia - the three marine taxa are in the same lineage. Hydrocharis + Limnobium are weakly sister to the rest, Stratiotes ditto to the remainder, and then Lagarosiphon strongly to the remainder, which are a strongly supported Egeria + Elodea and Blyxa + Ottelia. Les et al. (2006) in a four-gene analysis of all genera bar one, and including morphological characters, find Hydrocharitoideae to be sister to the rest of the family (support not given because only a single outgroup), Stratioitoideae sister (only moderate support, 72% bootstrap, all characters) to [Anacharidoideae + Hydrilloideae] (52%); all subfamilies were strongly supported. The morphologically very distinctive Naias is strongly supported (98%) as sister to Hydrilla in the combined analysis, although not in all individual analyses, and the two are notably far apart in the morphological analysis. Here I follow the classification suggested by Les et al. (2006).

Hydrocharis, apparently alone in the group, has a root epidermis that is of inner epidermal origin. Branching in Hydrocharitaceae needs more study; pseudodichotomous branching is quite common, and this is often interpreted as representing precocious axillary branching (Tomlinson 1982). There is also considerable variation in bracteole number and position (lateral; paired, etc.: see Eichler 1875) and Elodea is shown as having its carpels opposite the inner perianth whorl. Tanaka et al. (1997) note that flowers and axillary branches frequently arise from the same axil. The carpels may be more or less free (Weberling 1989 for references). The ovary in at least some taxa is filled with mucilage, but it is unclear if there are intra-ovarian trichomes (Rudall et al. 1998c). The mitochondrial nad1 intron 2 is absent in two representatives of this family (Gugerli et al. 2001), although just how widely this loss is spread is unclear.

General information is also taken from Cook (1998), Haynes, Holm-Nielsen et al. (1998), and Haynes and Holm-Nielsen (2001); for testa anatomy, see Shaffer-Fehre (1991a, b), and for pollination mechanisms, see Cook (1982: these correlated with pollen morphology and phylogeny, see Tanaka et al. (2004).

BUTOMACEAE Richard, nom. cons.   Back to Alismatales

Plant monopodial; flavonols?; leaves ± 2-ranked; inflorescence umbellate, with subtending bracts, (floral bracts 0); P whorls both petaloid, not identical, A 9, some latrorse, nectar from carpel flanks, G 6, plicate, fusion postgenital, placentation laminar, many crassinucellate ovules/carpel, secretion covers placentae, stigma ± decurrent; fruit a follicle; outer walls of exotestal cells thickened and with encrustations, tegmen persists; embryo and color?; n = 7, 8, 10, 11, 12, etc., chromosomes 3.7-8.3 µm long.

1[list]/1: Butomus umbellatus. Temperate Eurasia, naturalised in N.E. North America (Map: from Hultén & Fries 1986). [Photo - Habit © D. Woodland, Inflorescence © E. Parnis.]

• Butomaceae are aquatic monocots that may be recognised by their long, three-angled leaves and axillary, scapose, umbellate, bracteate inflorescence. The flowers are perfect and there are clearly two distinct perianth whorls although both are petaloid; the fruit is a follicle.

Stant (1967) reports crystals "in the form of small rods" in the diaphragm cells; she also suggests that the leaf of Butomus is equivalent to the petiole of Limnocharitaceae. There appear to be C-A primordia, with a pair of stamens differentiating first, and then a single stamen adaxial to that pair (Singh & Sattler 1974).

Much information is taken from Cook (1998).

Alismataceae + Limnocharitaceae: plant with latex; stomata with parallel divisions; leaves involute, with pseudopetiole, midrib, cross veins and an apical subepidermal pore; C thin, more or less crumpled in bud, evanescent, A centrifugal, pollen pantoporate, spinose, G free or connate basally, ovules tenuinucellate, embryo sac tetrasporic, nucellar cap +; fruit a follicle; embryo strongly curved, white; n = 7, 8.

There is often a residual floral apex remaining after the carpels have been initiated (seee Leins & Stadler 1973, also references below).

Details of relationships between Alismataceae and Limnocharitaceae, as well as within Alismataceae, are still rather unclear (Soros & Les 2002; Kato et al. 2003; Chen et al. 2004a, b); Alismataceae may well include Limnocharitaceae.

ALISMATACEAE Ventenat, nom. cons.   Back to Alismatales

(Corms, stolons); (unicellular or stellate hairs); flavone and phenolic sulphates, tannins +; (vessels 0); leaves 2-ranked to spiral, primary veins do not merge with each other, (inverted vascular bundles); (plant mon- or dioecious); inflorescence branches whorled; A 3-many, (pollen 0-3 porate - Caldesia), nectar at base of C, A, or P, or from staminodes or carpel flanks, G 2-many, partly ascidiate, 1(2-10 [Damasonium]) apotropous ovules/carpel, ovules basal-lateral; fruit also achenes; exotesta with outer wall thickened, tegmen ± obliterated or walls ± thickened; n = (5-13), chromosomes 2.4-14.4 µm long.

12[list]/81. Pantropical, also temperate (Map: see den Hartog 1957; Hultèn 1961; Meusel et al. 1965; Haynes & Holm-Nielsen 1997). [Photo - Flower, Echinodorus Flower, Fruit, Sagittaria Flower.]

• Alismataceae are laticiferous, aquatic herbs. Their floating or aerial leaves are petiolate and have a prominent midrib, parallel veins and also cross veins. Their petals are crumpled in bud and their staminate flowers usually have many extrorse anthers and their carpellate flowers have many free carpels. It is obvious from looking at the seeds that the embryo is strongly bent.

Stem-group Alismataceae are dated to ca 57 million years before present, crown group Alismaceae to ca 55 million years before present (Janssen & Bremer 2004).

Although there are often many carpels and stamens, organ initiation is basically whorled. Anther initiation may be centrifugal or centripetal, and the carpels initiate first in the antesepalous positions, sometimes on gynoecial bulges (Singh & Sattler 1972, 1973, 1977a; Charlton 2004 and references). Alisma and relatives have granular, not spinose pollen and nuclear not helobial endosperm. The pollen often contains starch.

Echinodorus is polyphyletic (Soros & Les 2002; see also Lehtonen & Myllys 2008).

Much information is taken from Haynes, Les and Holm-Nielsen (1998); for vegetative anatomy, see Stant (1964), for floral development, see Wang and Chen (1997).

Synonymy: Damasoniaceae Nakai

LIMNOCHARITACEAE Cronquist   Back to Alismatales

(Stolons +); flavone and phenolic sulphates, tannins 0; rhizome with endodermis; leaves spiral, primary veins merge with each other, colleters 0; inflorescence branches whorled; A 6-many, centrifugal, (outer members staminodial), usu latrorse, (pollen triporate; inaperturate), ?nectar, G 3-20, many ovules/carpel, placentation laminar, embryo sac monosporic, 4-nucleate, stigma ?; testa thin-walled, cells with upturned ends [Limnocharis], or with glandular hairs; n = (10), chromosomes 2.6-13.6 µm long.

[list]3/7. Pantropical (Map: see Haynes & Holm-Nielsen 1992). [Photo - Flower] [Photo - Flowers]

• Limnocharitaceae are laticiferous, aquatic herbs. Their floating or aerial leaves are petiolate and have a prominent midrib and parallel veins as well as cross veins. Their flowers have sepals, small to large but evanescent petals, many stamens (and also staminodes), and carpels with many ovules and laminar placentation. It is obvious that the seeds have a strongly curved embryo.

Development of the androecium is centrifugal; there are common stamen primordia as well as groups of gynoecial primordia opposite the sepals (Sattler & Singh 1977). The pores of the pollen grains have very irregular margins. The individual fruitlets of Limnocharis separate from the axis and float; seeds that they contain may be dispersed by this means.

Information is taken from Hooper and Symoens (1982) and Haynes, Les and Holm-Nielsen (1998); see Sattler and Singh (1977) and K.-M. Liu et al. (2002) for floral development.

Scheuchzeriaceae + Aponogetonaceae + Juncaginaceae + Posidoniaceae + Ruppiaceae + Cymodoceaceae + Zosteraceae + Potamogetonaceae: primary root poorly developed; P members with a single trace; chromosomes (0.5-2.3(-4.5) µm long.

The first branch in this clade (Aponogetonaceae versus the rest!) is dated to ca 98 million years before present (Janssen & Bremer 2004).

Aponogetonaceae and Scheuchzeriaceae are sister taxa, in turn sister to other members of the group, in a rbcL analysis of Kato et al. (2003).

SCHEUCHZERIACEAE F. Rudolphi, nom. cons.   Back to Alismatales

Plant irregularly sympodial; cyanogenic glucoside triglochinin +, flavonoids 0; stem endodermis +; stomata tetracytic; leaves 2-ranked, auriculate, with apical pore; inflorescence a raceme, bracts +; pollen in dyads, inaperturate, nectary 0, G 3(-6), plicate, basally connate, opposite outer P, plicate, fusion usually congenital, (1) 2 subbasal crassinucellate ovules/carpel, outer integument 5-6 cells across, inner integument ca 4 cells across; fruit a follicle; testa smooth, anatomy?; embryo with large cotyledon, green; n = 11, chromosomes 0.8-2 µm long; cotyledon not photosynthetic.

1[list]/1: Scheuchzeria palustris. N. Temperate to Arctic (Map: see Hultén 1961; Fl. N. Am. 22: 2000). [Photo - Habit.]

• Scheuchzeriaceae are small herbs of marshy places with distichous leaves; the open sheaths have auricles at the top and there is a little pore at the tip of the blade. The racemose inflorescence has large, leafy bracts and all the parts of the flowers (except the bases of the carpels) are free from one another.

Although Scheuchzeriaceae are chemically like Juncaginaceae, they are not otherwise particularly similar.

Information is taken from Haynes, Les et al. (1998).

Aponogetonaceae + Juncaginaceae + Posidoniaceae + Ruppiaceae + Cymodoceaceae + Zosteraceae + Potamogetonaceae: ?

There are suggestions that the "flowers" of all or many of the taxa in this group are pseudanthia (Rudall 2003b for references).

APONOGETONACEAE J. Agardh, nom. cons.   Back to Alismatales

Plant with a short rhizome or corm, apical meristems of vegetative axes bifurcating [?all]; vessels 0; articulated laticifers +; leaves spiral, involute, with pseudopetiole, midrib and cross veins, primary veins merge with each other, no tertiary veins, apex of old leaves with pore; plants usu. monoecious or dioecious; inflorescence spicate, bracts 0; (flowers monosymmetric), P 2-6, staminate flowers: A (-16; introrse; stamen pairs +;), staminodes present, microsporogenesis also simultaneous; carpellate flowers: (P 0), G 2-9, alt. P, plicate, septal nectaries + (0), 1-12 (unitegmic) basal ovules/carpel, nucellar cap +; fruit a follicle; coat mucilaginous, exotesta protective or not, endotegmen tanniniferous, or undifferentiated and translucent; embryo with large cotyledon, green or not; n = ?12, 16, 19, etc., chromosomes 0.7-2.3 µm long; cotyledon bifacial.

1[list]/43. Old World, esp. South Africa, largely tropical and warm temperate, esp. in Southeast Asia-Malesia a number of localities (not on map) where it is under suspicion of being introduced (Map: from van Bruggen 1985). [Photo - Aponogeton Flower © H. Wilson, Habit © R. Kowal.]

• Aponogetonaceae are water plants with petiolate leaves; the sometimes fenestrate blades have a midrib, parallel veins, and strong cross veins; the finest veins are reticulate. The spicate inflorescence has a long scape and the rather small flowers nevertheless have more or less conspicuous tepals.

A bract may form an hybrid organ with a tepal, so making the flower slightly monosymmetric, but separate bracts were not seen (Buzgo 2001). More pronounced monosymmetry occurs in flowers in which only two perianth members develop; these appear to be the abaxial pair, and in a monocot flower with "normal" orientation these would be members of the inner perianth whorl (see Singh & Sattler 1976b).

Some information is taken from van Bruggen (1998); for leaf development, see Gunawardena et al. (2004), for phylogeny, see Les et al. (2005).

Juncaginaceae + Posidoniaceae + Ruppiaceae + Cymodoceaceae + Zosteraceae + Potamogetonaceae: sulphated phenolic acids +, leucanthocyanins, flavones 0; leaf ± linear, base auriculate, ligulate; P 0 or reduced ["abaxial outgrowth" of A], anthers sessile, pollen inaperturate, nectary 0, carpels with complete postgenital fusion [sampling!].

For distribution of sulphated compounds, see especially McMillan et al. (1980).

JUNCAGINACEAE Richard, nom. cons.   Back to Alismatales

Apical meristems of vegetative axes bifurcating [?all]; O- and C-glycosyl flavones, cyanogenic glucoside triglochinin +; stem endodermis + or 0; (laticifers - Lilaea); stomata also tetracytic, with parallel divisons; leaves spiral, ± unifacial (subequitant), (ligules - Triglochin); inflorescence ± scapose spike or raceme, (flowers polygamous), bracts 0; flowers 1-3-merous, monosymmetric, "P" 0-4, 6, A 3-8, G 1 [3-10], weakly connate, fertile carpels oposite inner P, plicate, 1-few basal (apical, straight [atropous] - Maundia) crassinucellate ovules/carpel, outer integument 3< cells across, (styles long - some Lilaea); fruit schizocarpic, achenial (hooked, winged); exotesta and entegmen with cuticle, otherwise crushed; endosperm 0, nuclear, embryo with short thick hypocotyl and large cotyledon, color?; n = 6, 8, 15, etc., chromosomes 0.6-1.1 µm long; hypocotyl 0.

4[list]/15. Cosmopolitan, but largely coastal (Map: see Hultèn 1961; Meusel et al. 1965; Hultén & Fries 1986; Fl. N. Am. 22: 2000; FloraBase 2004). [Photo - Habit] [Photo - Fruit]

• Juncaginaceae are herbs of marshy places with more or less unifacial leaves and a scapose racemose or spicate inflorescence; all parts of the flower appear free.

Stem-group Juncaginaceae are dated to ca 82 million years before present, crown group Juncaginaceae to ca 52 million years before present (Janssen & Bremer 2004).

Imperfect flowers may lack a perianth (Lilaea) and either stamens or carpels; to a certain extent the number of parts in the flower is connected with flower size (Buzgo et al. 2006). The inner perianth whorl may be borne internal to outer stamens (Dahlgren et al. 1985). The abaxial median tepal is bract-like (Buzgo 2001; Buzgo et al. 2006). There is no evidence of pseudanthia in the family; terminal flowers are closer to being peloric (Buzgo et al. 2006). Seedlings of Triglochin have 2-ranked leaves.

Some information is taken from Arber (1925) and Haynes, Les et al. (1998); for alternative interpretations of the gynoecium, see Igersheim et al. (2001).

Synonymy: Heterostylaceae Hutchinson, Lilaeaceae Dumortier, Maundiaceae Nakai, Triglochinaceae Chevalier

Posidoniaceae + Ruppiaceae + Cymodoceaceae + Zosteraceae + Potamogetonaceae: aquatics; rhizome with endodermis; epidermis chlorophyllous; water pollination; carpels ascidiate [sampling!], 1 apical straight [atropous] ovule/carpel; fruit ± drupaceous; embryo with massive elongated hypocotyl, also prominent in seedling, collar or base of hypocotyl much enlarged.

The first split within this clade can be dated to ca 73 million years before present (note that the topology from which this date was taken is slightly different from that used in the tree above), and other divergence dates are given for members of this group (Janssen & Bremer 2004).

Underwater pollination, hypohydrophily, is common in this clade, and has been much studied (e.g. Pettit et al. 1980; Cox 1988; Cox et al. 1991).

This group is only poorly supported (Les et al. 1997).

Posidoniaceae + Ruppiaceae + Cymodoceaceae: ± marine; vessels 0; stomata 0; leaves 2-ranked; pollen filiform.

Posidoniaceae may have diverged from [Zosteraceae + Potamogetonaceae] ca 65 million years before present (Janssen & Bremer 2004).

Ruppiaceae are sister to [Posidioniaceae + Cymodoceaceae] in a rbcL analysis of Kato et al. (2003).

POSIDONIACEAE Hutchinson, nom. cons.   Back to Alismatales

Plant monopodial, with copious unlignified fiber strands; inflorescence pedunculate, branched-racemose, bracts 0; P 0, A 3, sessile, opening basally, connective shield-like, with prolongation [= P?], G 1, stigma asessile, complex; fruit a fleshy follicle [?: pericarp fleshy]; n = 10, dimorphic; seedling?

1[list]/9. Mediterranean, temperate Australia (Map: see den Hartog 1970).

• Posidoniaceae are marine "grasses" that are readily recognisable by the fibrous strands persisting along the monopodial rhizome and the branched-racemose inflorescences.

Information is taken from Kuo and McComb (1998).

Ruppiaceae + Cymodoceaceae: leaves serrulate; A 2.

RUPPIACEAE Horaninow, nom. cons.   Back to Alismatales

Plant monopodial, often in brackish or fresh water; sulphates?; endodermis?; leaves 1-veined, sheath not ligulate, ± auriculate [= "stipule"]; inflorescence terminal, spicate, bracts 0; A sessile, with abaxial outgrowth, pollen elongate-arcuate, G (2-)4(-16), stipitate, ovules also lateral, campylotropous, micropyle bistomal, stigma sessile, ± peltate; fruit an operculate drupelet; testa 2-layered, exotegmen cells large with branched protuberances from the walls, all becoming crushed; n = 8, 10-12, dimorphic, chromosomes 0.7-4.4 µm long.

1/1-10. More or less world-wide, apparently quite frequently gowing well away from the sea in all continents (Map: see Hultén 1961; Fl. N. Am. 22: 2000; Heywood 1978 [for the southern hemisphere]).

• Ruppiaceae are submerged aquatic plants growing in saline to fresh water that may be recognised by their 2-ranked, serrulate leaves with an obvious midrib and a sheathing base; the internodes are well developed.

Ruppiaceae are only doubtfully distinct from Cymodoceaceae (Les et al. 1997).

Some information is taken from Haynes, Holm-Nielsen et al. (1998); there are reports of nuclear endosperm (Johri et al. 1992).

CYMODOCEACEAE N. Taylor, nom. cons.   Back to Alismatales

Distinctive cyclitols; leaves serrulate at apex; plant monoecious or dioecious; inflorescence cymose, flowers in groups enclosed by bracts or solitary, P 0; staminate flowers: A [2], filament present, (microsporogenesis simultaneous - Thalassodendron); carpellate flowers: G 2, styles long, often branched, stigma long; fruit an achene or drupelet; testa 0; endosperm nuclear; n = 7, 8, 10, 14, 15; ?seedling.

5[list]/16. More or less tropical (to warm temperate), Australia in particular (Map: see den Hartog 1970; van Baloogy 1975). [Photo - Habit]

This family needs work. Note that Tomlinson (1982) described Thalassodendron as having a basal, anatropous ovule, while Takhtajan (1985) suggested that the ovules of Syringodium, although apical, were anatropous and straight [atropous]. Pollen of Amphibolis is up to 5 mm long. Cymodocea antarctica is viviparous, and the cotyledon is at most small (see Arber 1925).

Some information is taken from Kuo and McComb (1998: general); for cyclitols, see Drew (1983).

Zosteraceae + Potamogetonaceae: leaf with apical pore, (sheath closed); plant mono- or dioecious; P and A pair with single vascular trace.

Estimates of the time these two clades diverged range from ca 100 million years before present (Y. Kato et al. 2003) to ca 47 million years before present (Janssen & Bremer 2004).

ZOSTERACEAE Dumortier, nom. cons.   Back to Alismatales

Marine, main stems monopodial, adventitous roots unbranched; also flavone sulphates +; vessels 0; rhizome cortex with fibrous strands (not Phyllospadix) and vascular bundles; stomata 0; leaves 2-ranked, apical pore developing; inflorescence with spathe and spadix, spadix axis flattened, flowers two ranked, alternating on adaxial surface, bracts 0; staminate flowers: P 1 ["retinaculum"], A 1, anther thecae separate, deciduous, joined by divided connective, pollen filiform, (binucleate); carpellate flowers: G [2], appearing to be attached tranversely on pedicel, one fertile, outer integument to 7 cells across, style short, styles long, stigmatic; fruit achenial, ribbed; exotestal cells ± anticlinally and periclinally elongate, other cells persist, ± thickened or not, tegmen degenerates; n = 6, 9, 10, chromosomes 0.9-1.6 µm long; no primary root.

2[list]/14. Temperate to subtropical (Map: see den Hartog 1970; van Balgooy 1975). [Photo - Zostera Inflorescence © D. Woodland]

• Zosteraceae are sea grasses with leaf-opposed branches and flattened inflorescence axes (spadices) with flowers on the adaxial surface; the inflorescences are enclosed by a spathe. Most taxa have "retinacules", perhaps tepals or bracts, opposite the stamens.

Within Zosteraceae, divergence may have started ca 33 million years before present (Y. Kato et al. 2003).

All leaves on a plant are similar in morphology. Are there really two, bisporangiate/monothecal anthers? The course of endosperm development is unclear.

General information is taken from Kuo and McComb (1998) and Tomlinson and Poslusny (2001), reproductive morphology from Soros-Potruff and Posluszny (1995), and generic limits from Les et al. (2001); for a phylogeny, see Y. Kato et al. (2003).

POTAMOGETONACEAE Reichenbach, nom. cons.   Back to Alismatales

Freshwater plants, (apical meristems of vegetative axes bifurcating - Zannichellia); sulphated compounds 0, (flavone sulphates +, vessels 0 - Zannichellia); leaves spiral or opposite, involute, pseudopetiole, midrib and cross veins common, primary veins merge with each other, (margin serrulate), ligule basal, sheathing, (adnate to leaf base), auricules 0; inflorescence spicate, bracts 0 (+), (2-)4-merous; "P" clawed, adnate to A, G (1-)4(-8), alternating with P, ± stipitate, parlty ascidiate - or [Zannichellia] inflorescence proliferating sympodially; staminate flowers: P 0 or 3, A 1, 2-8-sporangiate; carpellate flowers: P tubular, or 3-4, G 1-8, when 3, opposite P, ovule ± pendulous, apotropous, straight [atropous] to campylotropous, stigma enlarged, peltate or infundibular with ± feathery margin; fruit a drupelet (berrylet); seed exotestal, or coat crushed [some Potamogeton, Zannichellia]; embryo coiled, white; n = 7, 12, 14-18, chromosomes 0.5-2.3 µm long.

4[list]/102: Potamogeton (60). Worldwide, esp. temperate (Map: see Hultén 1961; Meusel et al. 1965; Haynes & Holm-Nielsen 2003). [Photo - Habit, Potamogeton Inflorescence.]

• Potamogetonaceae are aquatic plants most of which have more or less petiolate leaves with midrib and cross veins; there is usually a conspicuous basal ligule. The inflorescence is densely spicate and the flowers have small tepals appearing to be borne on the backs of the stamens. The carpels are stipitate, as is particularly clear in Zannichellia, although that genus does not have a spicate inflorescence.

Within Potamogetonaceae, divergence may have begun ca 25 million years before present (Janssen & Bremer 2004).

Sattler (1962) and Singh (1965) considered the perianth and androecium to be distinguishable; there is a single trace to the P/A pairs.

Potamogeton in particular is a very important source of food for ducks in North America. Cross-pollination is by wind, or by pollen floating on the surface of the water. There is great variation in the leaf base, including the ligules (often called stipules), and of leaf shape both within and between species; some taxa of Potamogeton are heterophyllous, with submerged and floating leaves differing greatly in form. In Potamogeton the fruit floats and is photosynthetic.

Zannichellia, alone commonly with flavone sulphates, is rather weakly embedded within Potamogetonaceae (Les et al. 1997). Potamogeton is para- or polyphyletic (Les & Haynes 1995).

Much general information is taken from from Haynes (1978) and Haynes, Les et al. (1998); for the phylogeny and evolution of Potamogeton in particular, see Lindqvist et al. (2006).

Synonymy: Hydrogetonaceae Link, Zannichelliaceae Chevalier, nom. cons.