EXTANT SEED PLANTS

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

MAGNOLIOPHYTA

Plant woody, evergreen; lignans, O-methyl flavonols, dihydroflavonols, triterpenoid oleanane, non-hydrolysable tannins, quercetin and/or kaempferol +, apigenin and/or luteolin scattered, [cyanogenesis in ANITA grade?], lignins derived from both coniferyl and sinapyl alcohols, containing syringaldehyde [in positive Maüle reaction, syringyl:guaiacyl ratio less than 2-2.5:1], and hemicelluloses as xyloglucans; root apical meristem intermediate-open; root vascular tissue oligarch [di- to pentarch], lateral roots arise opposite or immediately to the side of [when diarch] xylem poles; origin of epidermis with no clear pattern [probably from inner layer of root cap], trichoblasts [differentiated root hair-forming cells] 0; stem with 2-layered tunica-corpus construction; wood fibers and wood parenchyma +; reaction wood ?, with gelatinous fibres; starch grains simple; primary cell wall mostly with pectic polysaccharides; tracheids +; sieve tubes eunucleate, with a sieve plate and cytoplasm with P-proteins, companion cells from same mother cell that gave rise to the sieve tube; nodes unilacunar [1:?]; stomata with ends of guard cells level with pore, paracytic, outer stomatal ledges producing vestibule; leaves with petiole and lamina [the latter formed from the primordial leaf apex], development of venation acropetal, 2ndary veins pinnate, fine venation reticulate, veins (1.7-)4.1(-5.7) mm/mm², endings free; flowers perfect, polysymmetric, parts spiral [esp. the A], free, development in general centripetal, numbers unstable; P not sharply differentiated, outer members not enclosing the rest of the bud, smaller than inner members; A many, with a single trace, introrse, filaments stout, anther ± embedded in the filament, tetrasporangiate, dithecal, with at least outer secondary parietal cells dividing, each theca dehiscing longitudinally by action of hypodermal endothecium, endothecial cells elongated at right angles to long axis of anther; tapetum glandular, binucleate; microspore mother cells in a block, microsporogenesis successive, walls developing by centripetal furrowing; pollen subspherical, binucleate at dispersal, trinucleate eventually, tectum continuous or microperforate, ektexine columellar, endexine thin, compact, lamellate only in the apertural regions; nectary 0; G free, several, ascidiate, with postgenital occlusion by secretion, few [?1] ovules/carpel, ovules marginal, anatropous, bitegmic, [outer integument often largely subdermal in origin, inner integument dermal], micropyle endostomal, integuments 2-3 cells thick, nucellus at apex of ovule 1-3 cells thick, megasporocyte single, megaspore lacking sporopollenin and cuticle, chalazal, female gametophyte four-celled [one-modular, nucleus of egg cell sister to one of the polar nuclei], stylulus short, hollow, cavity not lined by distinct epidermal layer, stigma ± decurrent, dry [not secretory]; P deciduous in fruit; seed exotestal; pollen germinating in less than 3 hours, siphonogamy, tube elongated, growing at 80-600 µm/hour, with callose plugs and callose-based walls, penetrating between cells, penetration of ovules within ca 18 hours, distance to first ovule 1.1.-2.1 mm; tube moves between nucellar cells, double fertilisation +, endosperm diploid, cellular [first division oblique, micropylar end initially with a single large cell, chalazal end more actively dividing], copious, oily and/or proteinaceous, embryo cellular ab initio, minute; germination hypogeal, seedlings/young plants sympodial; Arabidopsis-type telomeres [(TTTAGGG)_n]; whole genome duplication, single copy of LEAFY and RPB2 gene, knox genes extensively duplicated [A1-A4], AP1/FUL gene, paleo AP3 and PI genes [paralogous B-class genes] +, with "DEAER" motif, SEP3/LOFSEP and PHYA + C/PHYB + E gene pairs.

Evolution. Possible apomorphies for flowering plants are in bold. Note that the actual level to which many of these features, particularly the more cryptic ones, should be assigned is unclear, because some taxa basal to the [magnoliid + monocot + eudicot] group have been surprisingly little studied, there is considerable variation between families in particular for several of these characters, and also because details of relationships among gymnosperms will affect the level at which some of these characters are pegged. For example, if reticulate-perforate pollen is optimized to the next node on the tree (see Friis et al. 2009 for a discussion), it effectively makes the pollen morphology of the common ancestor of all angiosperms ambiguous... For other features such a a nucellus only one (Nymphaeales) to three cells thick above the embryo sac and a stylar canal lacking an epidermal layer, although plesiomorphous for basal grade angiosperms (Williams 2009), where on the tree a thicker nucellus and a stylar epidermal layer are acquired has not yet been indicated.

NYMPHAEALES [AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]: vessels + [one position], elements with elongated scalariform perforation plates; axial parenchyma diffuse or diffuse-in-aggregate; tectum reticulate-perforate [here?]; ?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, antipodal cells persisting; endosperm triploid; ?germination.

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

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

Phylogeny. 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. There is, however, acccumulating evidence that Ceratophyllales are sister to eudicots (for discussion, see immediately preceding Magnoliales).

[CERATOPHYLLALES + EUDICOTS]: ethereal oils 0.

Evolution. Soltis et al. (2008: a variety of estimates) suggest an age of divergence of Ceratophyllales and eudicots of 160-123 million years, while Magallón and Castillo (2009) give a age of 201 and 128 million years for relaxed and constrained penalized likelihood datings respectively..

The question is, how to optimise characters that are placed at or near 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 to answer unless, e.g., detailed studies of the development of the distinctive inaperturate Ceratophyllum pollen gives clues as to its derivation. Being an ancient aquatic lineage, Ceratophyllaceae have a very derived morphology. Thus it has been suggested that Ceratophyllaceae are sister to Chloranthaceae, as suggested by e.g. Duvall et al. (2006). Features common to that clade include: Leaves opposite, margin toothed; flowers small; G 1, ovule 1, pendant, straight, nucellar cap +; fruit indehiscent (see also Duvall et al. 2006). If Ceratophyllaceae were sister to monocots, features for that combined clade would include: 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. However, if Ceratophyllaceae are sister to eudicots, as now seems likely (Jansen et al. 2007; Saarela et al. 2007; Moore et al. 2007), any similarity in characters between Ceratophyllaceae and monocots that could be linked with a more or less aquatic habitat are likely to be parallelisms - and there are no morphological characters in particular linking Ceratophyllaceae with eudicots.

Chemistry, Morphology, etc. One might almost expect a submerged aquatic plant to lack ethereal oils...

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 [?or bracts] not vascularised, anthers 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 apical pendulous unitegmic ovule; seed coat ± obliterated; endosperm [with small initial micropylar cell] 0, suspensor 0. - 1 family, 1 genus, 1-2+ species.

Evolution. The distinctive fruits (with associated leaves) of Ceratophyllum are known from the Aptian and Albian onwards and are widely distributed (see Dilcher & Wang 2009 for references). Dilcher and Wang (2009) describe Domlesia, from deposits in Kansas of the end-Albian age some 100 million years ago, a plant that they think may be sister to Ceraytophyllum; note that it has a basal rather than an apical ovule.

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, plumule well developed; 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.

Chemistry, Morphology, etc. There is a ring of air canals in the stem outside the pericycle, and also a central air canal. 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). Shamrov (2009) described the gynoecium as being two-carpellate and syncarpous.

Some information is taken from Les (1993); see Iwamoto et al. (2003) for floral morphology.

Phylogeny. See Les (1989 and references) for species limits (unclear) and sectional groupings.