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.

SABIALES [PROTEALES [TROCHODENDRALES [BUXALES [GUNNERALES + CORE EUDICOTS]]]]  Back to Main Tree: ?

PROTEALES [TROCHODENDRALES [BUXALES [GUNNERALES + CORE EUDICOTS]]]: ?

TROCHODENDRALES [BUXALES [GUNNERALES + CORE EUDICOTS]]: benzylisoquinoline alkaloids 0; euAP3 + TM6 genes [duplication of paleoAP3 gene: B class], mitochondrial rps2 gene lost.

BUXALES [GUNNERALES + CORE EUDICOTS]: ?

For the loss of the rps2 mitochondrial gene, see Adams et al. (2002b), for duplication of the paleoAP3 gene, see Kramer et al. 2006), also the Trochodendrales page.

BUXALES Reveal  Main Tree, Synapomorphies.

Steroidal pregnan pseudoalkaloids +; true tracheids +; compression wood +; stomata cyclocytic; lamina margin entire; flowers small, imperfect; filaments ± dorsifixed, micropyle bistomal, styles stigmatic their entire length, with two crests; seed testal, with several cell layers; endosperm development?, embryo size? - 2/3 families, 5 genera, 72 species.

Stem group Buxales date to 121-117 million years before present (Anderson et al. 2005).

The stomata of Buxaceae, at least, may be described as being laterocytic (Baranova 1983).

Didymelaceae are sister to Buxaceae (representatives of both tribes were included) in the three-gene analysis of Worberg et al. (2007), although Hilu et al. (2003: matK [incomplete sequence] alone) found Didymeles to be embedded in a paraphyletic Buxaceae. Including Didymelaceae in Buxaceae is an option in A.P.G. II (2003). The poorly-known Haptanthaceae is tentatively included in Buxales.

Includes Buxaceae, Didymelaceae, ?Haptanthaceae.

Synonymy: Didymelales Takhtajan - Buxanae Reveal & Doweld

HAPTANTHACEAE C. Nelson   Back to Unplaced

Evergreen tree; cork ?; fibers storied; vessel elements with scalariform perforations; nodes ?; stomata ?; petiole bundle arcuate; hairs 0; leaves opposite, weakly pli-nerved at the base, margins entire, stipules 0; plant monoecious, inflorescences axillary, cymose, bracteoles 0; staminate flowers: P 0?, A 2, anther dorsifixed, pistillode 0; carpellate flowers: P ?4, staminodes 0, G [3], stipitate, placentation parietal, 8-15 bitegmic ovules/carpel, outer integument ca 5 cells across, styles 3, spreading, stigmatic their entire length; fruit unknown; n = ?

1/1: Haptanthus hazlettii. C. America, Honduras, not recollected despite several attempts.

This is an distinctive plant, somewhat reminiscent of Buxaceae. It has parietal placentation and odd staminate flowers originally described as consisting of a single stamen (Goldberg & Nelson S. 1989), but which have two lateral anthers each with two thecae attached their length to an elliptic structure with a single arcuate bundle (?very broad filament; ?prophyll); the endothecium is massive (Doust & Stevens 2005). The staminate flowers are borne superposed along the two branches of the inflorescence, the carpellate flower being central; this inflorescence is also unlike any others. Shipunov (2003) placed the family in his Violales (= Malpighiales here), close to Salicaceae and Lacistemataceae (see also Goldberg & Alden 2005), but a position somewhere in the eudicots near or in Buxales rather than in the core eudicots seems more likely.

See Goldberg and Alden (2005) for some anatomical details.

Didymelaceae + Buxaceae: inflorescence racemose; pollen also with endoapertures.

DIDYMELACEAE Leandri   Back to Buxales

Evergreen trees; hairs small, peltate; cork ?; pericyclic fibers 0; pith chambered, nodes ?; fibers +; petiole with three traces, the two lateral inverse; leaves spiral; plant dioecious; staminate flowers: P 0, A 2, connate basally, anthers extrorse, pollen tricolpate with 2-orate colpi; carpellate flowers: ?P 1, scale-like, G 1, 1(2) median epitropous ovules/carpel, integuments ± prolonged, outer integument fringed apically; fruit a drupelet furrowed on one side; ?rudimentary aril +, testa cell walls thickened; endosperm type?, 0, embryo large; n = ?

1[list]/2. E. Madagascar. [Photos - Inflorescence]

• Didymelaceae may be recognised by their spiral, entire, greenish-drying leaves, indumentum of small scales, and small flowers, the staminate flowers having two extrorse anthers and the carpellate flowers a single carpel with a long, oblique stigma.

There is a broad pith and at best late-developing cork (Leandri 1937); the axial parenchyma is replaced by lignified cells (Takhtajan 1997). Harms (1893) describes sclereids in the pericyclic position, and also cortical sclereids. Iridoids are reported by Sutton (1989); Mabberley (1997) describes the family as being glabrous. Floral morphology has recently been described by von Balthazar and Endress (2002a) and Von Balthazar et al. (2003). In carpellate flowers there is a little scale between the ovule and the bract; its morphological nature is unclear. The flowers may be borne in pairs with a small hump between them, perhaps the pairs represent a modified cymose unit, the hump being e reduced terminal flower.

For a general summary, see Köhler (2006).

BUXACEAE Dumortier, nom. cons.   Back to Buxales

Small evergreen trees to herbs; raffinose, stachyose + [phloem exudate], tannins 0; cork subepidermal or pericyclic; sieve tube plastids with protein crystalloids; secretory cells single or in branching rows; petiole bundles arcuate; cuticle waxes as curled rodlets or irregular platelets; stomata cyclocytic (laterocytic); leaves opposite (spiral), flat to curved, margins entire or toothed, (2ndary veins subpalmate); plant monoecious (dioecious); staminate flowers: P 2-4(5), not clearly separated from bracteoles, decussate, (A 3-many); carpellate flowers: P 6-20, at least some spiral, carpels completely fused, 2 apotropous ovules/carpel, outer integument 8-9 cells across, ovular obturator +, styles ± marginal, stigma dry or weakly secretory; seed carunculate or not, exotesta lignified, palisade, hypodermis often lignified; endosperm nuclear [Sarcococca] or cellular, +, (perisperm +), embryo short to long.

4[list]/70 - two tribes below. ± World-wide, although very scattered, not Arctic (Map: see Meusel et al. 1978). [Photo - Inflorescence, Fruits.]

Sarcococceae

(Nodes 1:3 - Sarcococca); no tanniniferous tissue in the flowers [?Didymelaceae]; staminate flowers: (P 0 - Styloceras), filaments conspicuous, pollen pantoporate, with crotonoid exine processes; carpellate flowers: bracts many, all spiral; G 2, (loculi divided), not nectariferous; fruit a drupe; testa multiplicative, endotegmen lignified [Sarcococca]; embryo with short radicle; n = 12-14.

3/22. E. Asia to W. Malesia, E. North America, N. South America.

Buxeae

(Cortical vascular bundles +); staminate flowers: pollen tri- to polycolpate, colpus with 2-4 endoapertures, or polyporate, pistillode with nectary (0); carpellate flowers: inflorescence with basal decussate "bracts"; G 3, median member adaxial, nectary between styles (0), micropyle endostomal; fruit an explosively-dehiscent capsule; embryo ± curved, radicle long; n = 14, 20.

1/30. Scattered, inc. Madagasacar, only Central America and West Indies in New World, not Australia nor much of Malesia.

• Buxaceae are generally monoecious evergreen herbs to small trees with exstipulate and often opposite leaves and rather small flowers with an inconspicuous perianth. The stamens are opposite the perianth, and the styles, stigmatic their entire length, are prominent and more or less spreading. The fruit is few-seeded, the mesocarp and endocarp separate, and the latter splits septicidally as well. In flower and fruit Buxaceae look rather like Euphorbiaceae s.l., but there is no columella in the fruit, unlike Euphorbiaceae.

Drinnan et al. (1991) described the fossil Spanomera from the Albian, some 98-113 million years before present; it is assignable here. Anderson et al. (2005) suggest that stem group Buxaceae date from 118-99 million years before present, crown group Buxaceae date from 111-63 million years before present.

The carpellate flowers have spirally inserted parts, but the basical floral construction of the family is perhaps dimerous (note that in the fossil Spanomera the carpellate flowers, too, may be dimerous, but there may also be five stamens opposite five tepals - Drinnan et al. 1991); this has suggested relationships with Trochodendraceae (Doyle 1999). However, as von Balthazar and Endress (2002) show, interpretation of inflorescence morphology is not easy, indeed, the nature of the paired "bracts" (?prophylls?!) below the carpellate flowers of Buxus is particularly unclear.

Buxus often has fiber strands in stem. All genera (but Styloceras is unknown) have three vascular bundles in the upper part of the petiole. Perianth parts have a single vascular bundle. Some species of Buxus have distinctive pollen with two or more orae per colpus that is rather like that of Didymelaceae; pollen in the family is variable (Köhler 2006 for references).

For nectary types, see Vogel (1998b), for fossil pollen, Doyle (1999), for phylogeny, von Balthazar et al. (2000) and von Balthazar and Endress (2002b), for inflorescence morphology, von Balthazar and Endress (2001, 2002a), for floral morphology, von Balthazar and Endress (2001, 2002b), and for a general summary, see Köhler (2006).

Synonymy: Pachysandraceae J. Agardh, Stylocerataceae (Pax) Reveal & Hoogland (staminate flowers lack a perianth, A many, carpels subdivided [as in Pachysandra] - 1 genus).