Plant a shrub or tree; true roots +, origin endogeneous, root cap +, apex multicellular; endodermis +; shoot apical meristem multicellular; lateral meristems +, cork cambium producing cork abaxially, vascular cambium producing phloem abaxially and xylem adaxially; lamina with mean venation density 1.8 mm/mm2 (to 5 mm/mm2).
EXTANT SEED PLANTS/SPERMATOPHYTA
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 derived from (some) sinapyl and particularly coniferyl alcohols, thus containing p-hydroxyphenyl and guaiacyl lignin units [so no Maüle reaction]; root xylem exarch, cork cambium deep seated; arbuscular mycorrhizae +; shoot apical meristem interface specific plasmodesmatal network; stem with vascular tissue around central pith [eustele], vascular bundles with interfascicular tissue, ectophloic, endodermis 0, xylem endarch; wood homoxylous, tracheids and rays alone, tracheid/tracheid pits circular, bordered; mature sieve tube/cell lacking functioning nucleus, sieve tube plastids with starch grains; phloem fibres +; stem cork cambium superficial; branches exogenous; leaves with single trace from vascular sympodium ["nodes 1:1"]; vascular bundles collateral [stem: phloem external; leaf: phloem abaxial]; stomata morphology?, pore opening in response to leaf hydration active, control by abscisic acid, metabolic regulation of water use efficiency, etc.; leaves with petiole and lamina, spiral, development basipetal, blade simple; axillary buds +, not associated with all leaves; prophylls two, lateral; plant heterosporous, sporangia borne on sporophylls; microsporophylls aggregated in indeterminate cones/strobili; true pollen +, grains mono[ana]sulcate, exine and intine homogeneous; ovules unitegmic, parietal tissue 2+ cells across, 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, developing after pollination, with cell walls, flagellae numerous; ovules increasing considerably in size between pollination and fertilization, female gametophyte endosporic, initially syncytial, walls then surrounding individual nuclei; seeds "large" [ca 8 mm3], but not much bigger than ovule, with morphological dormancy; embryo cellular ab initio, endoscopic, plane of first cleavage of zygote transverse, suspensor +, short-minute, embryo straight, shoot and root at opposite ends [allorrhizic], white, cotyledons 2; plastid transmission maternal; ycf2 gene in inverted repeat, two copies of LEAFY gene, PHY gene duplications [three - [BP [A/N + C/O]] - copies], nrDNA with 5.8S and 5S rDNA in separate clusters; mitochondrial nad1 intron 2 and coxIIi3 intron and trans-spliced introns present.
Lignans, O-methyl flavonols, dihydroflavonols, triterpenoid oleanane, non-hydrolysable tannins, quercetin and/or kaempferol +, apigenin and/or luteolin scattered, [cyanogenesis in ANITA grade?], S [syringyl] lignin units common [positive Maüle reaction - syringyl:guaiacyl ratio more 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, exodermis +; shoot apex with tunica-corpus construction, tunica 2-layered; reaction wood ?, associated gelatinous fibres [g-fibres] with innermost layer of secondary cell wall rich in cellulose and poor in lignin; starch grains simple; primary cell wall mostly with pectic polysaccharides, poor in mannans; tracheid:tracheid [end wall] plates with scalariform pitting, wood parenchyma +; sieve tubes enucleate, sieve plate with pores (0.1-)0.5-10< µm across, cytoplasm with P-proteins, cytoplasm not occluding pores of sieve plate, companion cell and sieve tube from same mother cell; sugar transport in phloem passive; nodes unilacunar [1:?]; stomata brachyparacytic [ends of subsidiary cells level with ends of pore], outer stomatal ledges producing vestibule, reduction in stomatal conductance to increasing CO2 concentration; lamina formed from the primordial leaf apex, margins toothed, development of venation acropetal, secondary veins pinnate, overall growth ± diffuse, venation hierarchical, fine venation reticulate, veins (1.7-)4.1(-5.7) mm/mm2, endings free; most/all leaves with axillary buds; flowers perfect, pedicellate, ± haplomorphic, parts spiral [esp. the A], free, numbers unstable, development in general centripetal; P not sharply differentiated, with a single trace, outer members not enclosing the rest of the bud, often smaller than inner members; A many, filament not sharply distinguished from anther, stout, broad, with a single trace, anther introrse, tetrasporangiate, sporangia in two groups of two [dithecal], ± embedded in the filament, with at least outer secondary parietal cells dividing, each theca dehiscing longitudinally, endothecium +, endothecial cells elongated at right angles to long axis of anther; tapetum glandular, cells binucleate; microspore mother cells in a block, microsporogenesis successive, walls developing by centripetal furrowing; pollen subspherical, tectum continuous or microperforate, ektexine columellate, endexine thin, compact, lamellate only in the apertural regions; nectary 0; G superior, free, several, ascidiate, with postgenital occlusion by secretion, stylulus short, hollow, cavity not lined by distinct epidermal layer, stigma ± decurrent, carinal, dry [not secretory]; ovules few [?1]/carpel, marginal, anatropous, bitegmic, micropyle endostomal, outer integument 2-3 cells across, often largely subdermal in origin, inner integument 2-3 cells across, often dermal in origin, parietal tissue 1-3 cells across [crassinucellate], nucellar cap?; megasporocyte single, hypodermal, megaspore tetrad linear, functional megaspore chalazal, lacking sporopollenin and cuticle; female gametophyte four-celled [one module, nucleus of egg cell sister to one of the polar nuclei]; ovule not increasing in size between pollination and fertilization; pollen binucleate at dispersal, male gametophyte trinucleate, germinating in less than 3 hours, pollination siphonogamous, tube elongated, growing between cells, growth rate 20-20,000 µm/hour, outer wall pectic, inner wall callose, with callose plugs, penetration of ovules via micropyle [porogamous], whole process takes ca 18 hours, distance to first ovule 1.1-2.1 mm; male gametes lacking cell walls, flagellae 0, double fertilization +, ovules aborting unless fertilized; P deciduous in fruit; seed exotestal, becoming much larger than ovule at time of fertilization; endosperm diploid, cellular [micropylar and chalazal domains develop differently, first division oblique, micropylar end initially with a single large cell, divisions uniseriate, chalazal cell smaller, divisions in several planes], copious, oily and/or proteinaceous; embryogenesis cellular; germination hypogeal, seedlings/young plants sympodial; dark reversal Pfr -> Pr; Arabidopsis-type telomeres [(TTTAGGG)n]; 2C genome size 1-8.2 pg [1 pg = 109 base pairs], whole genome duplication, ndhB gene 21 codons enlarged at the 5' end, 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 three copies of the PHY gene, [PHYB [PHYA + PHYC]].
[NYMPHAEALES [AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]]: wood fibres +; axial parenchyma diffuse or diffuse-in-aggregates; pollen monosulcate [anasulcate], tectum reticulate-perforate [here?]; ?genome duplication; "DEAER" motif in AP3 and PI genes lost, gaps in these genes.
[AUSTROBAILEYALES [[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]]]: vessel elements with scalariform perforation plates in primary xylem; essential oils in specialized cells [lamina and P ± pellucid-punctate]; tension wood +; tectum reticulate; anther wall with outer secondary parietal cell layer dividing; carpels plicate; nucellar cap + [character lost where in eudicots?]; 12BP [4 amino acids] deletion in P1 gene.
[[CHLORANTHALES + MAGNOLIIDS] [MONOCOTS [CERATOPHYLLALES + EUDICOTS]]] / MESANGIOSPERMAE: benzylisoquinoline alkaloids +; polyacetate derived anthraquinones + [?level]; outer epidermal walls of root elongation zone with cellulose fibrils oriented transverse to root axis; P more or less whorled, 3-merous [possible positiion]; embryo sac bipolar, 8 nucleate, antipodal cells persisting; endosperm triploid; ?germination.
[MONOCOTS [CERATOPHYLLALES + EUDICOTS]]: (extra-floral nectaries +); (veins in lamina often 7-17 mm/mm2 or more [mean for eudicots 8.0]); (stamens opposite [two whorls of] P); (pollen tube growth fast).
[CERATOPHYLLALES + EUDICOTS]: ethereal oils 0.
EUDICOTS: (Myricetin, delphinidin +), asarone 0 [unknown in some groups, + in some asterids]; root epidermis derived from root cap [?Buxaceae, etc.]; (vessels with simple perforation plates in primary xylem); nodes 3:3; stomata anomocytic; flowers (dimerous), cyclic; K/outer P members with three traces, ("C" +, with a single trace); A few, (polyandry widespread, initial primordia 5, 10, or ring, ± centrifugal), filaments fairly slender, anthers basifixed; microsporogenesis simultaneous, pollen tricolpate, apertures in pairs at six points of the young tetrad [Fischer's rule], cleavage centripetal, wall with endexine; G with complete postgenital fusion, stylulus/style solid [?here]; seed coat?
[PROTEALES [TROCHODENDRALES [BUXALES + CORE EUDICOTS]]]: plant woody; (axial/receptacular nectary +).
[TROCHODENDRALES [BUXALES + CORE EUDICOTS]]: benzylisoquinoline alkaloids 0; euAP3 + TM6 genes [duplication of paleoAP3 gene: B class], mitochondrial rps2 gene lost.
Age. Magallón and Castillo (2009) tentatively suggest an age of about 122.7 m.y. for this node, Vekemans et al. (2012: MRCA Buxales and Trochodendrales) an age of around (124.1-)122.6(-121.1) m.y. or a little less. The age for stem Trochodendrales in Wikström et al. (2003) is about (140-)135, 123(-118) m.y. - but c.f. sister group [B [T + CE]].
Evolution. Divergence & Distribution. Doyle (2013) is inclined to think that the evolution of 2-merous, wind pollinated flowers can be pegged to this node.
Genes & Genomes. For the paleoAP3 duplication, etc., see Lamb and Irish (2003), S. Kim et al. (2004b, 2005a), Zahn et al. (2005a), and especially Kramer et al. (2006); Kramer and Zimmer (2006) note that although the paleoAP3 gene has been found in Proteales and Sabiales, whether or not it occurs in Buxales and Trochodendrales remains unclear. EuAP3/PI are involved in stamen identity very much as paleoAP3/PI, but the former may be involved in petal development in core eudicots. For the loss of the rps2 mitochondrial gene, see Adams et al. (2002b), and for the duplication of the RPB1 and RPB2 genes, which may have occurred in the immediate ancestor of Trochodendrales, see Oxelman et al. (2004) and Luo et al. (2007). This latter is a complicated problem, since Buxaceae have no duplication in either gene and there has also been widespread loss of both genes. See the Gunnerales page for a genome triplication.
Phylogeny. For discussion on the position of Trochodendrales, see the Ranunculales page.
TROCHODENDRALES Cronquist Main Tree.
Stomata laterocytic; anthers valvate, latrorse, filaments thin; G laterally connate, nectariferous abaxially, 5 vascular bundles/carpel; 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, elongated; endosperm development? - 1 family, 2 genera, 2 species.
Note: Possible apomorphies are in bold. However, the actual level at which many of these features, particularly the more cryptic ones, should be assigned is unclear. This is partly because many characters show considerable homoplasy, in addition, basic information for all too many characters is very incomplete, frequently coming from taxa well embedded in the clade of interest and so making the position of any putative apomorphy uncertain. Then there is the not-so-trivial issue of how ancestral states are reconstructed...
Synonymy: Trochodendrineae Engler - Trochodendranae Reveal
TROCHODENDRACEAE Eichler, nom. cons. Back to Trochodendrales
Evergreen trees; flavonols +; petiole bundle arcuate; buds with scales; lamina toothed, secondary veins proceed to a clear, persistent cap, lateral veins also enter; cuticle waxes with nonacosan-10-ol a major component; flowers with cortical vascular system; pollen tectum reticulate-striate; G very slightly inferior; ovules with chalazal protrusion; seeds flattened, with marginal flange, chalazal hair-pin bundle +.
2/2 [list]. Southeast Asia, scattered.
Trochodendron Siebold & Zuccarini
Myricetin +; plant glabrous; pits bordered; vessels 0; young stem with separate vascular bundles; rays ca 12-seriate; nodes 1:1-7:7; ± branched sclereids +; leaves spiral, venation subpinnate; plant androdioecious, inflorescence terminal; P 0-5, minute, not vascularized; A many, ± spiral; G [(4-)6-11(-17)], with a secretion canal, placentation apical-axile, styluli erect, stigma decurrent in two crests; ovules many/carpel; (follicles also opening abaxially); seeds pendulous, endotesta sclerotic; endosperm cellular; n = 20.
1/1: Trochodendron aralioides. Japan to N. Taiwan (map: red, fossils blue [Japan - N.E. Honshu, not in the sea...], Pigg et al. 2001, 2007). [Photo - Collection, Inflorescences.]
Chalcones or dihydrochalcones +; secretory cells +; leaves two-ranked, lamina vernation supervolute, secondary veins palmate, leaf base broad, thin latero-basal flange enveloping axillary bud, lamina with palmate venation; inflorescence axillary, spicate; flowers small, 4-merous; P 4, vascular bundle rudimentary; A equal and opposite P; G , alternate with P, styluli short, spreading, placentation axile; ovules 5-6/carpel; testa multiplicative, 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).
Synonymy: Tetracentraceae A. C. Smith, nom. cons.
Age. Estimates for the divergence times of the two genera are (113-)106, 95(-88) m.y. Wikström et al. (2001) or (65-)20, 19(-7) m.y.a. (Bell et al. 2010).
Fossils of Trochodendraceae are known from since the late Cretaceous as Nordenskioldia, more properly Nordenskioeldia, close to Trochodendron. They are widely distributed around the northern hemisphere in the Eocene, and are sometimes at very high latitudes (Crane et al. 1991; Pigg et al. 2001, 2007; Taylor et al. 2009; Harrington et al. 2011). However, the hairpin loop in the seed is not found in at least some fossil Trochodendraceae (Crane et al. 1991, but c.f. 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 and Trochodendron, although both genera had long been considered to lack vessels (Hacke et al. 2007; Ren et al. 2007a; Li et al. 2011; c.f. Bailey & Thomopson 1918).
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. In Trochodendron, on the other hand, not only is nodal anatomy variable and the leaves on the adult plant have a narrow petiole and often lack axillary buds, in the young plant the leaves are more similar to those of Tetracentron (Bailey & Nast 1945; Nast & Bailey 1955). Although Baranova (1983) described both genera as having laterocytic stomata, Metcalfe and Chalk (1950) described and drew the stomata of Trochodendron as being laterocylic, while 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 both genera the adaxial side of the carpel develops greatly as the fruits ripen and so the style becomes basal on the abaxial side of the follicle.
See Nast and Bailey (1945) for flowers, fruits and summary, Endress (1986b) for floral morphology, Endress (1993) general, Wu et al. (2007) for perianth evolution and Chen et al. (2007) for floral morphology of Tetracentron; 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 sclereids 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 (c.f. 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 was 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 (see A.P.G. III 2009).