Asterids: tubes and pseudanthia

Abstract

Asterids are subdivided into two main groupings: basal asterids (a grade) consisting of Cornales and Ericales, and euasterids (with Lamiids and Campanulids) (Figs. 11.1, 11.2; e.g. Judd and Olmstead, 2004). Spichiger et al . (2002) distinguished between archaic asterids, superior hypogynous asterids and superior epigynous asterids. Characters common in a majority of taxa of asterids are sympetaly with adnate stamens (stamen-petal tube), unitegmic, tenuinucellate ovules, cellular endosperm formation, terminal endosperm haustoria, pollen that is released at the trinucleate stage, and the presence of iridoids (e.g. Judd and Olmstead, 2004; Soltis et al ., 2005). Apart from sympetaly, the other characters cannot be used in floral diagrams. Most taxa share the development of a ring primordium in early stages of development (Erbar, 1991) indicating a generalized syndrome of petal development (see p. 34). Core asterids (euasterids) share sympetaly, a bicarpellate gynoecium and haplostemony, while the basal orders Cornales and Ericales are much more variable with a basically diplostemonous androecium. Basal asterids: Cornales, Ericales Cornales The basalmost order of asterids (Fig. 11.2) contains six to seven families, with three main families Hydrangeaceae, Cornaceae and Loasaceae. All share small sepals, an inferior ovary, epigynous disc nectary, and often drupaceous fruits (Soltis et al ., 2005). Soltis et al . (2005) argued that the half-inferior ovary of Hydrangeaceae evolved from epigyny common in the clade. Most Cornales have free petals, with the evolution of a corolla tube in a few Loasaceae.