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.

Phylogeny. For discussion on the phylogenetic position of Trochodendrales, see the Ranuculales page.

TROCHODENDRALES Cronquist  Main Tree, Synapomorphies.

Filaments thin, anthers valvate, latrorse; G laterally connate, nectariferous abaxially, with 5 vascular bundles, ovules apotropous, integuments long, micropyle bistomal; fruit an aggregate of follicles, styles becoming ± basal on the outer surface; endotestal cells with slightly thickened walls, exotegmic cells thick-walled, tracheidal; endosperm development? - 1 family, 1 genus, 2 species.

Evolution. Magallón and Castillo (2009) tentatively suggest an age of about 122.7 million yeats for stem Trochodendrales.

Includes Trochodendraceae.

Synonymy: Trochodendrineae Engler - Trochodendranae Reveal

TROCHODENDRACEAE Eichler, nom. cons.   Back to Trochodendrales

Evergreen trees; flavonols +; idioblasts in cortex; buds with scales; stomata laterocytic; leaves toothed, secondary veins proceed to a clear, persistent cap, lateral veins also enter; cuticle waxes with nonacosan-10-ol a major component; tectum reticulate-striate; seeds flattened, with marginal flange, chalazal protrusion and hair-pin bundle.

2/2 [list]. Southeast Asia, scattered.

Trochodendron

Myricetin +; plant glabrous; pits bordered; vessels 0; young stem with separate vascular bundles; rays ca 12-seriate; nodes uni- to multilacunar; sclereids +; leaves spiral; plant androdioecious, inflorescence terminal; flowers with a cortical vascular system; P 0-5, minute; A many, ± spiral; G [(4-)6-11(-17)], with a secretion canal, placentation apical-axile; many ovules/carpel; styluli erect, stigma decurrent in two crests; (follicles also opening abaxially); seeds pendulous, endotesta sclerotic; endosperm cellular; n = 20.

1/1: Trochodendron aralioides. Japan to N. Taiwan (map: red, see above; fossils blue [Japan - N.E. Honshu, not in the sea], Pigg et al. 2001, 2007). [Photo - Collection, Inflorescences.]

Tetracentron

Chalcones or dihydrochalcones +; petiole bundles forming an annulus with flange bundles; secretory cells +; leaves two-ranked, supervolute, 2ndary veins palmate, petiole with thin latero-basal flange enveloping axillary bud, base broad; inflorescence axillary, spicate, flowers small; P 4, vascular bundle rudimentary, stamens equal and opposite perianth members, G [4], alternate with P, placentation axile, 5-6 ovules/carpel, styluli short, spreading; meso- and endotesta lignified, tegmen two layered, endosperm nuclear; n = 24.

1/1: Tetracentron sinense. China, Nepal (map: from Hara & Kanai 1964; fossils green, from Grímsson et al. 2008).

• Trochodendraceae are trees that may be recognised by their serrate, exstipulate leaves and their flowers in which there are several laterally connate carpels arranged in a whorl; nectary is poduced from the abaxial part of the carpel. The styles become displaced to the base on the abaxial side of the follicular fruits and the seeds are winged. Tetracentron has leaves with palmate venation, and the broad base of the leaf also completely encloses the axillary bud, while Trochodendron has leaves with palmate venation.

Evolution. Fossils of Trochodendron are known from since the late Cretaceous (Nordenskioldia, close to Trochodendron) and are widely distributed around the northern hemisphere (Crane et al. 1991; Pigg et al. 2001, 2007). However, the hairpin loop in the seed is not found in at least some fossil Trochodendraceae (Crane et al. 1991, but cf. Doweld 1998c); postgenital fusion of the carpels may not occur. Furthermore, in some fossils assigned to Trochodendron there are paired auricles or foliaceous stipels at the base of the lamina (Pigg et al. 2007). For the fossil record of the Tetracentron lineage, very largely Tertiary, see Grímsson et al. (2008).

Chemistry, Morphology, etc. Vessel elements with scalariform to scalariform-reticulate perforation plates have recently been reported from Tetracentron (Ren et al. 2007). In Tetracentron the petiole becomes round towards the base, and there is a marginal flange that tightly and totally envelops the axillary bud; the base of the petiole is broad and the scar encircles much of the stem. Note that although Baranova (1983) described both genera as having laterocytic stomata, Metcalfe and Chalk (1950) described and drew the stomata of Trochodendron as being laterocylic; the stomata are of Trochodendron are cyclocytic, according to Carlquist (1982).... The micropyle of Trochodendron is described as being endostomal in Johri et al. (1992) and Endress and Igersheim (1999), but it looks bistomal in Takhtajan (1991). In the follicles of both genera the adaxial side of the carpels becomes much developed as the fruits ripen and so the styles become basal on the abaxial side.

See Endress (1986b, 1993) for details and Wu et al. (2007) for perianth evolution; Rix and Crane (2007) provide general information about Tetracentron.

Previous Relationships. The relationships of the two genera included in Trochodendraceae have been somewhat obscure, although their apparent lack of vessels had long typed them as being primitive angiosperms. Endress (1986b) compared the scereids of Trochodendron and the secretory cells of Tetracentron with the cells secreting ethereal oils in magnoliids, etc., and linked the two genera with Cercidiphyllaceae (Saxifragales) and Eupteleaceae (Ranunculales) in an expanded Trochodendrales (cf. also Takhtajan 1997 and Thorne 2007 in part). Kai-yu et al. (1993) suggested that Tetracentron should be put in its own order.

Classification. Including Tetracentraceae in Trochodendraceae is an option in A.P.G. II (2003). The two families do have quite a lot in common, as is clear from the fairly lengthy ordinal description, and since both are monotypic, combination is in order.

Synonymy: Tetracentraceae A. C. Smith, nom. cons.