Taxonomy
of Flowering Plants - LECTURE
NOTES - Spring, 1998
Hugh
D. Wilson - rm. 306,
Butler Hall
1, 6, 8 April 1998
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 that 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 unique 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:
Gentianales
Asclepiadaceae
Solanales
Solanaceae
Convolvulaceae
Cuscutaceae
Polemoniaceae
Scrophulariales
Scrophulariaceae
Lamiales
Boraginaceae
Verbenaceae
Lamiaceae
(Labiatae)
Rubiales
Rubiaceae
Asterales
Asteraceae
(Compositae)
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