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Within the Asteridae (“Sympetalae Tetracyclicae”) two main developmental patterns can be distinguished as regards the formation of corolla tubes, namely “early” and “late sympetaly”. Since the character “ontogeny of sympetaly”, after intensive studies, proved to be valuable for systematic considerations, we now recognize two blocks of orders within the Asteridae (and related groups): the Asteridae A‐block and the Asteridae B‐block (Figs. 82 and 83). By and large this bipartition referring mainly to the corolla tube development corresponds well with major lineages indentified by recent molecular data (see, e.g., Chase et al., 1993). Asteridae A‐block is characterized predominantely by “late sympetaly” the “early sympetaly” in Rubiales and Oleales can be interpreted as derived within this block or can be linked with that in Asteridae B‐block. Asteridae B‐block is uniform throughout in its “early sympetaly”. In this block it is a primitive character, as judged from its occasional occurrence in the choripetalous Cornales and Apiales (Apiaceae, Araliaceae, Pittosporaceae), which can be regarded as ancestral for block B.

Families of the Campanulales-Asterales2omplex are characterized by special mechanisms for secondary pollen presentation: pump mechanism, brushing mechanism, deposition mechanism, cup mechanism and combination of cup mechanism with brushing mechanism. These different mechanisms are based on three successive events: elongation of the filaments, opening of the anthers, elongation of the style. The diversity of the mechanisms arises through different auxiliary structures such as an indusium, hairs or an anther tube, and the relative rate and time of filament and style growth. An advantage of secondary pollen presentation lies in the prolongation of the male phase of anthesis through portioned pollen release. A probable phylogeny of the different mechanisms of secondary pollen presentation is proposed (Fig. 7).

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