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.

[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]] : carpels plicate, occlusion by congenital fusion; embryo sac bipolar, 8 nucleate; endosperm triploid.

MONOCOTS [CERATOPHYLLALES + EUDICOTS]: (stamens opposite [two whorls of] P).

The age of this clade is perhaps 147-143 million years before present (Leebens-Mack et al. 2005).

Relationships between the lineages immediately above the basal pectinations in the main tree, the ANITA grade (Amborellales, Nymphaeales and Austrobaileyales here), have recently been clarified. The topology of the main tree in this area thus differs somewhat from that in A.P.G. (2003). For further information, see the discussion immediately preceding the Magnoliales, i.e. the magnoliid clade; Chloranthales, eudicots, and monocots are the other clades involved.

Given the very derived morphology of Ceratophyllales, identifying characters that are synapomorphies with other groups is difficult. Thus it has been suggested that Ceratophyllaceae are sister to Chloranthaceae, as suggested by e.g. Duvall et al. (2006). Features for that clade include: Leaves opposite, margin toothed; flowers small, G 1, ovule 1, pendant, straight [atropous], nucellar cap +; fruit indehiscent (see also Duvall et al. 2006). If Ceratophyllaceae were sister to monocots, "plant herbaceous; primary root at best weak; vascular bundles in stem closed [no interfascicular cambium developing]; vessels in stem and leaves 0; (leaf margin spiny toothed); microsporogenesis successive" might be a set of synapomorphies for the combined clade. Indeed, characters like leaf margin and microsporogenesis are consistent with an association between monocots and Ceratophyllaceae, but even if monocots are basally plants of wet habitats, with some of their distinctive features associated with this habitat and also found in Ceratophyllales, the latter are surely much more highly derived in many features than any common ancestor with the monocots. If Ceratophyllaceae are sister to eudicots, as now seems likely, any similarity in characters between Ceratophyllaceae and monocots that could be linked with a more or less aquatic habitat are likely to be parallelisms.

Given the more probable position of Ceratophyllales as sister to eudicots (for discussion, see immediately preceding Magnoliales), the question is, how to optimise characters that are placed at the eudicot node. Are some of these to be placed below the node [Ceratophyllales + eudicots]? Did their common ancestor have tricolpate pollen? Had it already lost ethereal oils? These are going to be very difficult questions indeed to answer unless, e.g., detailed studies of the development of the distinctive inaperturate Ceratophyllum pollen gives clues as to its derivation.

[CERATOPHYLLALES + EUDICOTS]: ethereal oils 0.

CERATOPHYLLALES Bischoff  Main Tree, Synapomorphies.

Aquatic herb; mycorrhizae absent; delphinidin +, alkaloids; roots 0; vessels 0; nodes?; stomata 0; leaves opposite, margins spiny-toothed; plant monoecious, flowers extraxillary, alternating with leaves; P not vascularised [?or bracts], A extrorse, arrangement unclear, connective apically produced, tapetum amoeboid, microsporogenesis ?successive, pollen inaperturate, exine much reduced, tubes branched, G 1, postgenital fusion by secretion, with 1 straight [atropous] apical unitegmic ovule; seed coat ± obliterated; endosperm [with small initial micropylar cell] 0, suspensor 0. - 1 family, 1 genus, 1-2+ species.

Synonymy: Ceratophyllanae Reveal & Doweld

CERATOPHYLLACEAE Gray, nom. cons.   Back to Ceratophyllales

Cuticle wax crystalloids 0; leaves dichotomously divided or not, one vegetative bud per node; P 6-13, whorled, basally connate, A 3(?)-46, ± sessile, tapetal cells uninucleate, nucellar cap +, style quite long, stigma small, at base of lateral groove; fruit achenial, spiny; endosperm 0, embryo large, green; n = 12.

1[list]/ca 6 (Map: see Vester 1940; Hegi 1965; Hultén 1971; Les 1989; Wilson 2007).  World-wide. [Photo - Habit © from D. Les website, Fruit © H. Wilson]

• Ceratophyllaceae may be recognised by their whorled, spiny-toothed, often dichotomously-branched leaves; their small, sessile flowers (even the perianth and connective have spiny teeth); and their distinctive, spiny, achenial fruits.

Species limits are unclear.  The distinctive fruits (with associated leaves) are known from the Aptian and Albian.

Although the leaves are whorled, there is only a single vegetative bud and usually only a single floral bud per node. The flowers are borne on the same orthostichy as the vegetative buds; the latter alternate their positions at each node, hence the floral buds will be lateral to the leaves (Rutishauser 1999).

Some information is taken from Les (1993); see Iwamoto et al. (2003) for floral morphology and Les (1989 and references) for species limits and sectional groupings.