Taxonomy of Flowering Plants - LECTURE NOTES
Hugh D. Wilson

The Asteridae

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.

Elements of the Asteridae are well marked by the presence of sympetaly and distinguished from sympetalous Dilleniidae by an androecium with stamens either equal to or less than the number of corolla lobes and positioned between the corolla lobes.  Other distinguishing features that occur in many of the larger, temperate families include a bicarpellate gynoecium and epipetalous stamens.  Cronquist indicates:
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)
    Lamiaceae  (Labiatae)
    Asteraceae (Compositae)

Return to Lecture Notes, the Biology 301 homepage, the Liliopsida, or the Rosidae
22 Oct 2010