The Subclass Asteridae, includes 11 orders, 49 families and nearly 60,000 species. Species diversity is comparable to that of the Rosidae, but differentiation at the family level is less than that of either the Rosidae or Dilleniidae. About a third of the species in this subclass are in the single family Asteraceae. This most specialized and diverse dicot family is comparable to the monocot family Orchidaceae in terms of class-level phylogenetic position, level of adaptive modification, and species diversity.
The Asteridae are the most advanced subclass of dicotyledons, and possibly the most recently evolved (only the Caryophyllidae may be more recent). More than any other subclass, they exploit specialized pollinators and specialized means of presenting the pollen. It seems likely that the rise of the Asteridae is closely correlated with the evolution of insects capable of recognizing complex floral patterns.The subclass is roughly organized by Cronquist into two lineages or clusters of orders (diagram above). One is marked by a dominance of hypogyny and the other, terminated by the Asterales, by epigyny.
Our coverage of the Asteridae will include:
Scrophulariales (APG circumscription)