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CORE EUDICOTS: flowers rather stereotyped: 5-merous, parts whorled, K and C distinct, K with 3 traces, A = 2x K, (often numerous, but then often fasciculate and/or centrifugal in development), pollen tricolporate, [G 5], [3] also common, compitum +, placentation axile, stigma not decurrent; endosperm nuclear; fruit dry, dehiscent, loculicidal [when a capsule]. [Back to Index]

The age of the core eudicot clade has been suggested to be 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 eudicot fossil flower is from the Cretaceous-Cenomanian, 96-94 million years ago (Basinger & Dilcher 1984). 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 those in other angiosperms (Magallón & Sanderson 2001).

Sepals usually have three traces and petals have one. As indicated in the characterisation above, taxa that have flowers with many stamens are scattered throughout the core eudicots. A number of these taxa initially have only five or ten primordia, in the former case, the primordia usually arise opposite the petals, rather than alternating with them. Numerous individual stamen primordia then develop from these few primordia, and development is often centrifugal (cf. magnoliids, the ANITA grade); at maturity, the stamens themselves may be more or less connate or in fascicles (see esp. Corner 1946b; Weberling 1989; Leins 2000 and references). Note, however, that there may be considerable variation in staminal development between closely related multistaminate taxa (e.g. Hufford 1990; Ge et al. 2007). Flowers with many stamens are much less common in the asterid I + II clade (q.v. for discussion) and there polyandry appears to be of a rather different nature. Chase (2005) noted that in Santalales some floral 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 polyandry in the eudicots, and seed coats with a mechanical layer more than a single cell thick occur throughout BLAs, but again, seed coats of the asterid I + II clade are rather different usually being one or two layers thick.

This clade is strongly supported, e.g. Chase et al. (1993), D. Soltis et al. (12003a), and Nandi et al. (1998), although Gunnerales (q.v.) have in the past also been included in core eudicots; Gunnerales and core eudicots are here considered sister taxa simply to make the eudicot clade readily characterisable (the floral morphology of Gunnerales is unlike that of core eudicots, but more like that of Proteales, etc.). Relationships within core eudicots are unclear. As things stand, there is a major basal polychotomy there, and there is in fact little support for the positions of some of the orders assigned below to clades of this polychotomy, such as Dilleniales with Caryophyllales, Vitales and in particular Saxifragales with rosids. 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). 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. Soltis et al. (2007a) found the relationships [Saxifragales [Vitales + rosids]], both groupings with 1.0 p.p. (see also Jansen et al. 2007; Moore 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