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.

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

TROCHODENDRALES [BUXALES [GUNNERALES + CORE EUDICOTS]]: mitochondrial rps2 gene lost.

BUXALES [GUNNERALES + CORE EUDICOTS]: ?

GUNNERALES + CORE EUDICOTS: Ellagic and gallic acids common, cyanogenesis via phenylalanine, isoleucine or valine pathways; micropyle?; PI-dB motif +, small deletion in the 18S ribosomal DNA common.

CORE EUDICOTS:  Back to Main Tree

Root apical meristem closed; flowers rather stereotyped: 5-merous, parts whorled, K and C distinct, K with 3 traces, A = 2x K, internal to the C whorl, (numerous, but then often fasciculate and/or centrifugal), pollen tricolporate, (nectary disc +), [G 5], [3] also common, compitum +, placentation axile, stigma not decurrent; endosperm nuclear; fruit dry, dehiscent, loculicidal [when a capsule]; euAP1 + euFUL + AGL79 genes [duplication of AP1/FUL or FUL-like gene], PLE + euAG [duplication of AG-like gene: C class], SEP1 + FBP6 genes [duplication of AGL2/3/4 gene].

It has been suggested that petals in the core eudicots are generally derived from tepals, perhaps ultimately bracts, not from stamens (with some exceptions: Ronse de Craene 2007). There are quite a number of gene duplications known from this general area, perhaps a whole genome duplication is involved (e.g. Litt & Irish 2003; Kramer et al. 2004; Kim et al. 2004; Zahn et al. 2005b; Howarth & Donoghue 2006; especially Kramer & Zimmer 2006; Shan et al. 2007). However, note that not all major core eudicot groups have been sampled for the euAP1 gene, the situations in Santalales and Gunnerales being unknown; there has been another duplication of this gene (and also of the AGL1/2/3 gene) perhaps immediately below this node, but above the Ranunculales node, and the roles these genes may have in many eudicot groups is unknown. However, the eu AP1clade includes key regulators that have been implicated in the specification of perianth identity (Litt & Irish 2003).

The age of the core eudicot clade is some 113 million years (Leebens-Mack et al. 2005, but see sampling), while Anderson et al. (2005) suggest a similar figure (stem group to 116 million years old, diversification by ca 109 million years before present). The oldest known fossil is from the Cretaceous-Cenomanian, 96-94 million years ago (Basinger " Dilcher 1984).

Sampling of variation in the root apical meristem is poor, and possible reversals (for which, see Groot et al. 2004) have not been placed on the tree. Lee et al. (2004) suggest that the CRABS CLAW gene is expressed in core eudicot nectaries (including extrafloral nectaries), or at least in the rosids and asterids that they sampled; it was not expressed in nectaries of Ranunculaceae, and what happens in Proteaceae (with axial nectaries, like rosids - see Smets 1988) is unfortunately unknown.

As indicated in the characterisation above, taxa with polyandrous flowers are scattered throughout the core eudicots, although much less common in the asterid I + II clade (q.v. for discussion) where polyandry appears to be of a rather different nature. Chase (2005) noted that in Santalales some parts, particularly stamens, might have several whorls, and this perhaps suggested that canalisation of floral development was less than in some other core eudicots; whether Santalales really are different in this respect from other core eudicot group remains to be established. The occurence of ellagic acid has a similar distribution as does that of seed coats with a mechanical layer more than a single cell thick; again, the asterid I + II clade may be rather different from the rest.

This clade is strongly supported, e.g. Chase et al. (1993), D. Soltis et al. (1997, 1999, 2003a), Hoot et al. (1998), and Nandi et al. (1998), but support is rather weaker in Zhu et al. (2007). although Gunnerales (q.v.) have in the past also been included in core eudicots; Gunnerales and core eudicots are here considered sister taxa.

Although the core eudicot clade is well supported, relationships within it are unclear. D. Soltis et al. (2003a) in a four-gene analysis suggested that Berberidopsidales are sister to the rest of the core eudicots, but there was only 54% jacknife support for this position. Santalales were associated with asterids, while Saxifragales and Vitales linked with [Dilleniales + Caryophyllales], but with still less support. In general, this is an area of considerable uncertainty. As things stand, there is a major polychotomy in core eudicots, and even some of the orders assigned to clades here (Dilleniales with Caryophyllales, Saxifragales and and to a certain extent Vitales with rosids) in fact have had rather poor support for their positions. Thus in some studies Dilleniaceae are sister to Caryophyllales, but with only very moderate support; D. Soltis et al. (2003a) provides rather stronger (83% jacknife) support for this position (see also Soltis et al. 2007a). It is also possible that Caryophyllales + Dilleniales and Santalales form a clade (D. Soltis et al. 2000); Carlquist (2006) suggested that non-bordered perforation plates was a possible similarity between Santalales and Caryophyllales. Caryophyllales were linked with with asterids in a large 18S ribosomal DNA analysis (Soltis et al. 1997), albeit with only weak support (see also Hilu et al. 2003). In recent studies using whole chloroplast genomes (Jansen et al. 2006a, esp. 2006b; Hansen et al. 2007; Cai et al. 2007; Ruhlman et al. 2006; Jansen et al. 2007; Moore et al. 2007) support for this position is stronger, however, Berberidospidales, Dilleniales, Santalales and Saxifragales were not included. [Caryophyllales + Santalales] were sister to asterids in some analyses in a study that focused on the position of Cynomoriaceae and Balanophoraceae (Nickrent et al. 2005), but again the sampling was only moderate. In a study using the mitochondrial gene matR, Caryophyllales were again sister to asterids, but with very little support; in other analyses including a reduced sampling and two chloroplast genes Santalales and Dilleniales were also in the area, but with little support (Zhu et al. 2007). In the combined morphological and molecular study of Nandi et al. (1998) the position of Caryophyllales is uncertain, but this is perhaps partly because the ovules of Rhabdodendraceae, there sister to all other Caryophyllales, were interpreted as being unitegmic; recent work suggests that Rhabdodendraceae are not sister to all other Caryophyllales, but are embedded in the order (see Caryophyllales page).

Hilu et al. (2003: matK analysis alone, although Schumacheria [one member of Dilleniaceae included in the study] was firmly associated with Ericales...) found possible relationships [Rosids [[Dilleniacaeae + Vitaceae] [Saxifragales [Santalales [Berberidopsidales [Caryophyllales + Asterids]]]]]]. Nickrent et al. (2005) also found the position of Saxifragales to be particularly uncertain, although Vitales again tended to go with rosids. Recently, Soltis et al. (2007a) found a grouping [Saxifragales [Vitales + rosids]], both groupings with 1.0 p.p. (see also Zhu et al 2007, but little support). Studies on the duplication of the RPB2 gene and subsequent loss of one of the copies (Oxelman et al. 2004; Luo et al. 2007) suggest that Saxifragales and Rosids are linked by loss of the -I copy, which also has occured in Santalales and Caryophyllales, but not Vitales, Berberidopsidales, Gunnerales or Dilleniales, which have all lost the RPB2-D copy. The variation pattern is complex - and this is without worrying about what is going on within the asterids. Saxifragales and Vitales were successively siter to all eudicots minus Gunnerales (mitochondrial gene only), or to all rosids, but with little support (Zhu et al. 2007). Palaeohexaploidy seems to link Vitales with rosids, but the samping in major core eudicot clades is very poor (Jaillon, Eury et al. 2007), and the implications of this paleohexaploidy in groups suspected of undergoing subsequent bouts of genome duplications in terms of gene copy numbers is unexplored.

All in all, a postion of Vitales as sister to Rosids seem probable (see that page for more details and characters), but, other than that, everything seems somewhat up in the air. For direct links to the other clades possibly involved, see Caryophyllales, asterids, Dilleniales, Crossosomatales, Saxifragales, Santalales, Vitales; in some cases there is further discussion immediately following or preceding the orders just mentioned.

For general information on core eudicot diversification, see Magallón et al. (1999); most of the estimates of percentage diversity of clades are taken from this work. The diversification rates of many of the clades are higher than the rate in other angiosperms (Magallón & Sanderson 2001).

BERBERIDOPSIDALES Doweld   Main Tree, Synapomorphies.

Tension wood?; crystals +; petiole bundle annular; stomata cyclocytic; filaments stout; style +; seed endotestal; endosperm development?, embryo? - 2 families, 3 genera, 4 species.

There is good support for this clade in a three-gene tree (e.g. D. Soltis et al. 1999); for stomatal morphology, see also P. Soltis and D. Soltis (2004). Carlquist (2003b) details the extensive if largely plesiomorphic similarities in the wood of the two families. Possible synapomorphies, however, include the strong differences between the procumbent cells of the multiseriate parts of the rays and the square to upright cells in the uniseriate portions and also the dark-staining deposits in axial parenchyma and rays. Other details of the vegetative anatomy show (apomorphic?) similarities between the two. Aextoxicon has few druses but numerous rhombic crystals presumably of calcium oxalate; Baas (1984) reported crystals in the leaves of all three Berberidopsidaceae, although druses seem to be commonest.

Includes Aextoxicaceae, Berberidopsidaceae.

Synonymy: Berberidopsidanae Thorne & Reveal

AEXTOXICACEAE Engler & Gilg, nom. cons.   Back to Berberidopsidales

Tree; chemistry?; true tracheids +; sclereids +; pith heterogeneous; indumentum of peltate scales; leaves opposite, conduplicate, entire; plant dioecious; inflorescence a raceme, (in threes, branching from basal prophylls); flowers (4) 5 (6)-merous, enveloped by bracteoles, K thin, deciduous, C broadly clawed, reniform nectary glands alternating with A; staminate flowers: A = and opposite K, filaments relatively stout, G vestigial; carpellate flowers: staminodia +, G [2], arrangement?, one locule empty, 2 pendulous apotropous ovules/carpel, micropyle endostomal, inner integument 5-7 layers across, nucellus strongly beaked, style ab?axially curved, apically bilobed; fruit a dry drupe, 1-seeded; seeds carunculate, ruminate, coat tanniniferous, ca 6 cells thick, cell walls thin; endosperm +, ?development, embryo long, curved, ± transverse, cotyledons flattened, cordate-orbicular; n = ?

1[list]/1: Aextoxicon punctatum. C. Chile (Map: from Donoso Z. 1994). [Photos - Flower, Flower, Flower, Flower, Fruit, Habit]

• Aextoxicaceae are dioecious evergreen trees that can be recognised by their opposite, entire exstipulate leaves that are covered with peltate scales and by their pendulous, racemose inflorescence. The petioles are almost pulvinate at the apex and the base and the lamina appears to be minutely peltate. The flower buds are covered by bracteoles and when they fall off, the almost scale-like sepals fall off with them.

Sclereids are found in all vegetative parts of the plant; those of the leaf blade are about half the thickness of the blade in length. The stomata are weakly actinocylic, with 5-7 subsidiary cells. The pith is notably heterogeneous. Although the stigma is bilobed, the bicarpellary construction of the gynoecium should be confirmed. The endocarp appears to split particularly readily along two vertical lines. The embryo is more or less transverse to the long axis of the seed.

Aextoxicaceae were included in Euphorbiales (Takhtajan 1997), and have also been linked with Saxifragales (Qiu et al. 1998).

For some anatomy, see Pax and Hoffmann (1917), for ovule morphology, see Mauritzon (1936), and for a general account, see Kubitzki (2006b). For fruit and stem anatomy, see Gentry et al. 53436, for leaf anatomy, see Solomon & Solomon 4420.

BERBERIDOPSIDACEAE Takhtajan   Back to Berberidopsidales

Evergreen woody scramblers; cyclopentenoid cyanogenic glycosides +, ellagic acid 0; cork?; fibers non-septate, pits bordered; (stomata bicyclic); leaves spiral, involute [Berberidopsis], 2ndry veins palmate, margins spiny-toothed or entire; inflorescences terminal; P (9-)12(-15), spiral, all except the outer petaloid, or K and C distinct, disc lobed, nectariferous, A 6-many, whorled or irregular, filaments short, anthers inserted along connective, connective with apical prolongation, pollen also tricolpate, G [3, 5], placentation parietal, 2-many epi- or pleurotropous ovules/carpel, micropyle bistomal, integuments ca 4 cells across, style stout, stigma punctate to slightly lobed; fruit a berry, K deciduous (persistent - Streptothamnus); (seed with chalazal arilloid - Streptothamnus), exotesta enlarged, fleshy, (inner mesotestal cells sclereids), endotestal cells crystalliferous, palisade, lignified, (exotegmen weakly developed, fibrous, lignified), endotegmen subpersistent; endosperm copious, ?development, embryo short; n = ?

2/3. Chile, E. Australia (Map: from Veldkamp 1984). [Photo - Habit, Flower/Fruit.]

• Berberidopsidaceae are woody scramblers that can be recognised by their exstipulate, sometimes spiny-toothed leaf blades with palmate venation; the veins run straight into the spines, when present. The fruit is a berry crowned by the persistent style base.

Leaves of Berberidopsis are weakly involute in bud and are not at all imbricated. In Streptothamnus the disc is absent, or perhaps it is to be found between the stamens and the gynoecium.

Berberidopsidaceae were included in Flacourtiaceae by Cronquist (1981) and in Violales by Takhtajan (1997).

Some information is taken from van Heel (1979, 1984: seed, pollen), Baas (1984: anatomy), Takhtajan (1992: seed), Ronse De Craene (2004: development of Berberidopsis corallina; note that it is difficult to see how floral development here is a "link" in the evolution of the flower of core eudicots, cf. also Kubitzki 2006b; Ronse De Craene 2007), and Kubitzki (2006b: general).