Core eudicots are a strongly supported clade, which represents 70% of all Angiosperms (Fig. 8.1; Soltis et al.,2005). Pentamerous flowers with a differentiation of a calyx and corolla are generalized, and there are good indications that a bipartite perianth, two stamen whorls and isomerous carpel whorl represent a condition acquired very early in the clade. However, lack of resolution among major lineages of core eudicots does not allow for a clear understanding of floral evolution, although progress is being made in solving this issue.

Gunnerales and Berberidopsidales

Gunnerales

The small order consists of two monogeneric families, Gunneraceae and Myrothamnaceae. Recent molecular analyses (e.g. Soltis et al., 2003) have placed Gunnerales as the sister group of all core eudicots. Gunneraceae have traditionally been associated with Haloragaceae (e.g. Schindler, 1905), mainly because their reduced flower morphologies look similar. The dimerous floral Bauplan of Gunnerales tends to be more similar to the basal eudicot grade, such as Buxales or Trochodendrales, than to the core eudicots and this has led to a questioning of the origin of pentamery from dimerous ancestors at the base of core eudicots (Ronse De Craene, 2004; Wanntorp and Ronse De Craene, 2005). Within Gunneraceae there is a general pattern to floral reduction and unisexual flowers, and it appears structurally difficult to derive pentamerous flowers from a prototype such as Gunnera (Wanntorp and Ronse De Craene, 2005; Ronse De Craene and Wanntorp, 2006).