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.

Relationships of the main groups within commelinids are unclear; for further information, see discussion preceding Dasypogonaceae, also Zingiberales and Poales.

POALES + COMMELINALES + ZINGIBERALES: Primary cell wall mostly with glucurono-arabinoxylans; endosperm starchy.

COMMELINALES + ZINGIBERALES: Inflorescences with many-flowered cincinnal [rather zig-zag cyme] branches; tapetum invasive or plasmodial.   Back to Main Tree

The stem group dates to ca 116 million years before present, divergence of the two clades to ca 114 million years before present (Janssen & Bremer 2004), while the figures in Wikström et al. (2001) are 87-83 and 81-73 million years before present respectively, while Bremer (2000b: largely fossil calibrations) dates the stem group to ca 108 million years before present, divergence to ca 84 million years before present.

In previous studies this group has sometimes been rather weakly supported (e.g. Chase et al. 2000a; Davis et al. 2004: Givnish et al. 2006b, one gene), although it has 100% support in the multi-gene analysis of Graham et al. (2006) and Chase et al. (2006). Tapetal variation in those few Zingiberales studied is extensive (Prakash et al. 2000; cf. Furness & Rudall 2001). There are several kinds of monosymmetry, especially in Zingiberales.

For phenyphenalenones, see Otálvaro et al. (2002), for monosymmetry, see Rudall and Bateman (2004).

COMMELINALES Dumortier  Main Tree, Synapomorphies.

Mycorrhizae absent; (phenyphenalenones +); vessel elements scalariform; cuticle waxes not as aggregated rodlets; (flower enantiostylous); seed coat testal and tegmic; endosperm abundant, helobial, cell wall formation in small chalazal chamber precedes that in large micropylar chamber. - 5 families, 68 genera, 812 species.

Stem-group Commelinales are dated to ca 114 million years before present, divergence within the group to ca 110 million years before present (Janssen & Bremer 2004); the corresponding dates in Wikström et al. (2001) are 81-73 and 71-66 million years before present respectively.

For relationships, see Givnish et al. (1999), Hopper et al. (1999), Graham et al. (2006) and Chase et al. (2006); Graham (in Graham et al. 2002) noted that there was very strong support for the grouping [Haemodoraceae + Pontederiaceae]. Janssen and Bremer (2004) suggest a rather different - and perhaps unlikely - set of relationships - [Philydraceae [Hanguanaceae [Haemodoraceae [Commelinaceae + Pontederiaceae]]]], and the dates below are based on this topology; Givnish et al. (2006b: ndhF gene only) also find Philydraceae to be sister to other Commelinales, but with little support.

Tapetal raphides are known from Commelinaceae, Philydraceae and Haemodoraceae, but their general distribution is unclear (Hardy & Stevenson 2000; Prychid et al. 2003a); there may be systematically interesting variation in the pattern of endothecial thickenings (Manning 1996). A five base pair insertion in the matK gene in members of Hanguanaceae and Pontederiaceae was found by Tamura et al. (2004), it was absent in Haemodoraceae, but no other taxa were sampled.

There has been much discussion over the position of Hanguanaceae, which in morphological analyses tends to cluster - sometimes quite strongly - with Zingiberales, although it lacks the inferior ovary of members of that order. Molecular analyses, on the other hand, suggest the inclusion of Hanguanaceae in Commelinales. Thus Givnish et al. (1999: rbcL) found that Hanguanaceae were sister to Commelinaceae, while Rudall et al. (1999: general) found Hanguanaceae to show a rather strong association with Zingiberales; the former position is accepted here (see also Davis et al. 2004).

Includes Commelinaceae, Haemodoraceae, Hanguanaceae, Philydraceae, Pontederiaceae.

Synonymy: Haemodorales Hutchinson, Hanguanales Reveal, Philydrales Dumortier, Pontederiales J. D. Hooker - Commelinanae Takhtajan, Pontederianae Reveal - Commelinidae Takhtajan

Commelinaceae + Hanguanaceae: cotyledon not photosynthetic.

COMMELINACEAE Mirbel, nom. cons.   Back to Commelinales

Rather succulent herbs; 6-hydroxyflavonoids +; vessels also in stem; hairs uniseriate; stem with swollen nodes; (prophylls lateral); leaves spiral (2-ranked), midrib prominent, sheath closed; andromonoecy common; inflorescences axillary (terminal), (boat-like bracts conspicuous); flowers open one day, P = K + C, C deliquescent, septal nectaries 0, (G [2]), 1-many ortho- to campylotropous thinly crassinucellate ovules/carpel, (outer integument 3< cells across), micropyle (exo)/endotegmic; (seeds uniseriate), endotesta silicified; endosperm nuclear, embryo marginal; n = 4<; collar rhizoids and coleoptile +.

40[Genera List]/652. Tropical and temperate.[Photos - Collection]

Cartonematoideae (Pichon) G. C. Tucker

SiO₂ bodies 0; stem collenchyma 0; raphide canals next to veins or 0; stomata paracytic or tetracytic; glandular microhairs 0, although plant glandular pubescent; inflorescence racemose, or one flower/cincinnus[!]; flowers sessile, yellow; fruit a berry; most of testa sloughed off; collar short, mesocotyl +, primary root strong; n = 12.

2/12. Mostly Australian, Triceratella Zimbabwe.

Synonymy: Cartonemataceae Pichon, nom. cons.

Commelinoideae Eaton

Cyanidin 3,7,3'-triglucoside +; stem collenchyma +; vessel elements with simple perforations, also in stem and leaf; stem with narrow cortex and endodermis-like sheath enclosing vascular bundles that connect only at the nodes; (SiO₂ bodies +); raphide canals between veins; stomata tetracytic, etc.; 3-celled glandular microhairs +; (leaves involute); (inflorescence axillary; prophyll lateral); flowers (obliquely monosymmetric; enantiostylous), blue, pink or white (yellow), (C connate; T in two series), A 1-6, (adnate to C), filaments often with dense uniseriate hairs, (connective [much] expanded), staminodes often 2-4, attractive, antipodals in embryo sac degenerate early [not Tinantia], polar nuclei fuse early; seed operculum ["embryotega"] testal, with a micropylar collar [position varies]; collar roots +; n =4<, often "large".

38/640: Commelina (170), Tradescantia (70), Aneilema (65), Murdannia (50), Cyanotis (50). Tropical, also temperate, not Europe (Map: see Heywood 1978; Fl. N. Am. 22: 2000; FloraBase 2004). [Photo - Flower] [Photo - Flower]

A monophyletic Commelineae and Tradescantieae can be recognised, with Floscopa (chromosomes <3 µm long), previously included in Tradescantieae, as sister to both (Givnish 2003). Commelineae have stomata with 6 subsidiary cells, spiny pollen and chromosomes ca 1-5 µm long; monosymmetric flowers are commonest here and hairs, if present, are not moniliform. Tradescantieae have stomata with 2-6 subsidiary cells, moniliform hairs and chromosomes ca 2-10µm long (cf. Judd et al. 2002); flowers with tepals (i.e. not differentiated into sepals and petals) are commonest in this clade. Wade et al. (2006) provide a subtribal classification of Tradescantieae based on a two-gene analysis; some subtribes are paraphyletic and the position of Palisota is still unresolved.

Synonymy: Ephemeraceae Batsch, Tradescantiaceae Salisbury

• Commelinaceae are herbs with rather soft and fleshy leaves; these have closed cheaths and may be involute in bud. The inflorescences usually consist of many-flowered helicoid cymes that are often subtended by large, leafy bracts; they are quite often leaf-opposed. The flowers usually last for one day only and are frequently blue or pink; when they are monosymmetric they are usually held with the median petal in the abaxial position. The filaments are often conspicuously hairy.

Stem group Commelinaceae are dated to ca 89 million years before present, divergence within it to ca 62 million years before present (Janssen & Bremer 2004), however, members of Cartonematoideae were not included in the study, so the latter date reflects divergence within Commelinoideae. Also, the topology of the tree on which this date is based is different from that used here.

Leaf-opposed inflorescences and those that perforate the leaf sheath as they emerge (as in Buforrestia) occur in the family. Enantiostyly is uncommon. In Dichorisandra the bracteoles are more or less lateral and the plane of symmetry of the flower is transverse, in other taxa it may be oblique (e.g. Eichler 1875). In at least some Commelinaceae the inner tepals have only a single trace. Weldenia has a long floral tube. Variation in androecial development is extreme, and in some taxa staminal development in centrifugal, a variant of obdiplostemony (Hardy & Stevenson 2000b). Indehiscent geocarpic fruits may be produced by Commelina bengalensis and Tapheocarpa; Mabberley (1987) suggested that some taxa may have a small second cotyledon. The cotyledon can be of the dropper type (Tillich 1995). Seedling leaves and often those at the base of axillary shoots are often 2-ranked even in those taxa with spiral leaves predominating in the vegetative plant.

A morphological phylogeny shows little resolution, although anatomical characters gave significantly more support for the rbcL phylogeny than did othet kinds of characters (Evans et al. 2000, cf. Evans et al. 2003). Perhaps not surprisingly, most taxa with strongly monosymmetric flowers form a clade, but Triceratella is widely separated from Cartonema, which is sister to the rest of the family. Evans et al. (2000) discuss the variety of pathways of stomatal development found in the family. Givnish (2003, summary tree only, no support values) emphasised the discordance between relationships suggested by morphological data, which did not retrieve a monophyletic Commelineae and Tradescantieae, largely because of high homoplasy of androecial characters, and molecular (rbcL) data, which did find these tribes to be monophyletic (with the exception of Floscopa, see above; Calisia [Tradescantieae] had a similarly isolated position in the morphological analyses). Evans et al. (2003: rbcL phylogeny, Triceratella not studied) also note conflict between morphology and molecules.

Some information is taken from Tomlinson (1966: anatomy), Jones and Jopling (1972: cytology), Stirton and Harborne (1980: anthocyanins - see cyanidin 3,7,3'-triglucoside distribution, but Cartonematoideae not sampled), Faden and Hunt (1991: general, classification of family), Faden (1998: general) and Hardy and Stevenson (2000a: development of Cochliostemon).

HANGUANACEAE Airy Shaw   Back to Commelinales

Plant sympodial; hairs multicellular, branched; mucilage canals +; leaves spiral, with petiole, midrib and cross veins; plant dioecious; inflorescence branched-spicate, flowers sessile; T pseudomonocyclic, small; staminate flowers: filaments broadened and connate at very base, pollen inaperturate, exine spinulose, pistillode +; carpellate flowers: staminodes nectar-secreting, intra-ovarian trichomes +, 1 basal straight [atropous] tenuinucellate ovule/carpel, epidermal cells elongated, style ± 0, stigmas 3, sessile; fruit a 1-seeded berry; seed bowl-shaped [placenta inside]; mesotesta and endotesta sclerified; endosperm type?, embryo small; n = ca 24, 36, 45; primary root well developed.

1[list]/6. Sri Lanka, South East Asia to Palau and N. Australia (Map: see Hewson 1986). [Photo - Fruit]

• Hanguanaceae are robust terrestrial herbs that have petiolate leaves with a midrib, many parallel veins, and prominent cross veins. The inflorescence is a panicle with sessile, small, and undistinguished flowers. The fruit is a single-seeded berry, and the seed itself is bowl-shaped as it comes to surround the placenta during development.

Hanguanaceae diverge from other Commelinales ca 104 million years before present (Janssen & Bremer 2004).

Raphides may occur, but they are rare (Prychid & Rudall 1999). Takhtajan (1985) illustrated a massively-thickened tegmen.

Information is taken from Tillich (1996: seedling), Bayer et al. (1998b: general), Tillich and Sill (1999: general), Givnish et al. (1999: rbcL), and Rudall et al. (1999: general).

Philydraceae [Haemodoraceae + Pontederiaceae]: SiO₂ bodies 0; styloids +; T with tannin cells, sclereids in placentae; T persistent in fruit.

PHILYDRACEAE Link, nom. cons.   Back to Commelinales

Proanthocyanins +; hairs often wooly; leaves usu. 2-ranked, equitant, isobifacial-ensiform; inflorescence racemose, groups of flowers [?arrangement] in axils of spathe-like bracts; flowers open for one day, enantiostylous, T petaloid, outer members 2, large [adaxial = 2 outer T plus adnate adaxial inner T all fused], inner T 2, lateral, small, A 1, abaxial member of outer whorl, septal nectaries 0, many ovules/carpel, funicular obturator +, stigma large; exotesta with thick cellulose walls, endotegmen tanniniferous, operculum tegmic; endosperm also with crystalline aleurone bodies, embryo long; n = 8, 16, 17; cotyledon linear, bifacial, collar rhizoids +.

4[list]/5. Australia (all genera) to Southeast Asia (Map: from Adams 1987; Hamann 1998b).

• Philydraceae can be recognised by their two-ranked, isobifacial-ensiform leaves - although Philydrella lacks these vegetative characters - inflorescences with wooly hairs, and their distinctive monosymmetric flowers. These have a two-merous perianth, the outer whorl usually being much larger than the inner, and a single stamen.

Stem group Philydraceae are dated to ca 110 million years before present, divergence within the crown group to ca 47 million years before present (Janssen & Bremer 2004).

Information is taken from Tillich (1994 - seedlings) and Hamann (1998 - general).

Haemodoraceae + Pontederiaceae: phenylphenalenones +; endothecial cells with base-plates, ektexine not tectate or columellate.

For phenylphenalenones, see Otálvaro et al. (2002), for the base plates of endothecial cells, see Manning (1996: absent in Commelinaceae, unknown for other families, sampling very poor).

HAEMODORACEAE R. Brown, nom. cons.   Back to Commelinales

Rhizomatous (cormose); fructans, chelidonic acid, flavones +; (vessels also in stem and leaf); leaves 2-ranked, equitant, isobifacial; cyme [usu.] bifurcated, prophyll ± lateral; flowers (large), plane of symmetry transverse to oblique; (T tube +), (connective appendages +), exine (1-)2(-3)-layered [no foot layer], G inferior, 1-many straight [atropous] ovules/carpel, placentae swollen, (nucellar cap +), micropyle (exo)/endostomal; cells of testa (and tegmen) variously elongated, ± thin-walled, operculum 0; embryo small/minute.

14[list]/116 - two subfamilies below. Tropics and warm temperate regions (Map: from Heywood 1978 [Africa]; MacFarlane et al. 1987 [Australia]; Maas & Maas-van der Kamer 1993 [America]; Fl. N. Am. 26: 2002 [N. America]).

1. Haemodoroideae Arnott

(Bulbs), roots red; tannins 0; hairs with distinctive basal cells; flowers enantiostylous, tannin cells 0, usu. glabrous, A 3 [opposite inner P] (1 - Pyrorrhiza; staminodes +), G superior [secondarily]; seeds often flattened, pubescent or marginally winged; cotyledon not photosynthetic, hypocotyl at most short; n = 12, 15, 19-21.

8/39: Haemodorum (20). Tropics and warm temperate regions, not in southern South America, only southern Africa, in S.E. Asia not W. of Wallace's Line. [Photo - Flower, Fruit, Flower]

Synonymy: Dilatridaceae M. Roemer, Wachendorfiaceae Herbert, Xiphidiaceae Dumortier

2. Conostylidoideae Lindley

SiO₂ sand +; (epidermal walls thickened), hairs branched; (leaf margin spiny); flowers usu. pubescent, P connate or not, (pseudomonocyclic; valvate; monosymmetric; A adnate to P), pollen 2-3 or 7-8 porate; (fruit indehiscent or a schizocarp); (seeds ridged); cotyledon photosynthetic, hypocotyl +, primary root well developed; n = 4-8, 11.

6/80: Conostylis (50). S.W. Australia. [Photo - Flower]

Synonymy: Conostylidaceae (Bentham) Takhtajan

• Haemodoraceae may be recognised by their 2-ranked, equitant isobifacial leaves, their inflorescences, which are often rather elongated bifurcated helicoid cymes, their sometimes monosymmetric and/or enantiostylous flowers with inferior ovaries, and their roots, which in Haemodoroideae have a distinctive red color.

Stem group Haemodoraceae are dated to ca 98 million years before present, divergence within the crown group to ca 81 million years before present (Janssen & Bremer 2004). Seed-eating bugs of the Hemiptera-Lygaeidae-Blissinae are known from Haemodoraceae from South Africa; most bugs of this clade are sap-eaters (Slater 1976). The restriction of Conostylidoideae to SW Australia is remarkable; Hopper et al. (2006) discuss the diversification of this group, in particular, of Conostylis.

The median petal is abaxial and the median carpel adaxial in monosymmetric flowers of Haemodoroideae such Wachendorfia, i.e., the flowers are inverted, while in Anigozanthus zygomorphy is evident as a slit down one side of a tube formed by the six connate tepals - the plane of symmetry must necessarily be slightly oblique here. As Eichler (1880) noted, if flowers are examined early in development, Wachendorfia has flowers with transverse symmetry, while in Anigozanthus they are oblique. Taxa like Xiphidium have a more or less differentiated perianth with the two whorls each fully encircling the apex and the three stamens are borne opposite the petals, while taxa like Anigozanthus have six stamens individually opposite the six perianth lobes (see illustrations in Simpson 1990). The ovary may be secondarily superior (Simpson 1998a, b); the septal nectaries are found below the point of insertion of perianth. There is a lot of variation in basic floral organization in this relatively small family! The outer periclinal wall of the testa is thick.

For the phylogeny of the family, which has been quite extensively studied and integrated with anatomical and morphological data, see Hopper et al. (1999) and Simpson et al. (2006), for the phylogeny of Conostylidoideae, see Hopper et al. (2006).

Some additional information is taken from Simpson (1988, 1990).

PONTEDERIACEAE Kunth, nom. cons.   Back to Commelinales

Water or marsh plants; vegetative stems indeterminate; (vessels also in stems); styloids or prismatic crystales 0 (+); neighbouring cells of stomata with oblique divisions; leaves spiral or spiro2-ranked (whorled), petiolate or not, 2ndaries transverse, sheath open or closed, often long-ligulate [= "stipules" sheathing to minute], colleters +; inflorescence subtended by two bracts; flowers open for one day, tristyly, enantiostyly, monosymmetry all common, obliquely monosymmetric [Pontederia cordata], T ± undifferentiated, pseudomonocyclic, marcescent (large), (4, 3), mostly blue or yellow, ± connate, A adnate to T, (1, 3, 4; staminodes 2), of different lengths, filaments hairy, pollen 2- or 3-sulcate, (septal nectaries 0; placentation parietal; 1 carpel fertile, with one ovule), septal nectary +/0, micropyle bistomal, stigma small, dry; (fruit an achene surrounded by P base); exotestal cells box-like, elongated, endotestal cells thin, elongated tranversely, operculum 0?; embryo large; n = (7) 8(-13); cotyledon linear, bifacial, collar rhizoids +.

9[list]/33: Heteranthera (11). Tropics, also temperate, esp. New World (Map: ; Fl. N. Am. 26: 2002). [Photos - Collection]

• Pontederiaceae are aquatic or marsh plants - sometimes annuals - with sheathing leaf bases that are often differentiated into a petiole and blade with many parallel veins, the blade of the younger leaf then encircles the petiole of the older leaf. The inflorescence has two bracts, either/both leaf-like and/or sheathing, and the marcescent, monosymmetric flowers are either basically blue or yellow.

Stem group Pontederiaceae are dated to ca 89 million years before present, divergence within the crown group to ca 39 million years before present (Janssen & Bremer 2004).

In Heteranthera, Eichornia s. str. and Pontederia s. str. (at least) the blade of the leaf of the axillary shoot completely encircle the main stem in bud, or the blade of the young leaf completely encircles the petiole of the next oldest leaf - this may be a unique arrangement (see also Eichler 1880) and so to be added to the apomorphies of the family. Although Hydrothrix gardneri appears to have whorled, linear leaves, only one leaf has a short, sheathing ligule; the others have narrower bases and are borne inside the sheath (Rutishauser 1999). Lunau (2006) suggests that the yellowish spot on the median-adaxial tepal member mimics a stamen.

Considerable work has been carried out on the floral biology of Pontederiaceae, where tristyly, enantiomorphy and monosymmetry (Pontederia cordata, at least, is obliquely monosymmetric) are all well known. Graham and Barrett (1995) discussed the evolution of the breeding system, while Barrett and Graham (1997) outlined the phylogeny and diversification of the family and Kohn et al. (1996) the evolution of reproductive features, however, there were problems of rooting the phylogenetic tree (see also Graham et al. 1998, esp. 2002). In the enantiostylous Monochoria there are five smalll stamens with yellow anthers and one large stamen with a blue anther (Wang et al. 1995 for pollination).

Eichornia currently is hopelessly paraphyletic, Pontederia and Monochoria being embedded in it (Graham et al. 1998). Simpson and Burton (2006) discuss the evolution of features of floral anatomy in the family, including outgroups; the embedded [Pontederia + Reussia} not only have single, apical ovules in the single fertile carpel and an achene surrounded by perianth, but they are the only members of the family to have styloids or prismatic crystals. Other features they studied also correlate with the clades of Barrett and Graham (1997).

Information is taken from Tomlinson (1982: colleters), Tillich (1994: seedlings), Cook (1998: general) and Strange et al. (2004: floral anatomy).

Synonymy: Heterantheraceae J. Agardh