Subclass:
Rosidae
Links to Family Pages:
Subclass consisting of 116 families, and more than 60,000 species of angiosperms - the largest subclass in terms of number of families and about the size of the subclass Asteridae in number of species. They are more advanced than the Magnoliidae by being syncarpous and less advanced than the Asteridae by being largely polypetalous rather than sympetalous or having more than two fused carpels. The Rosidae has been distinguished from the Dilleniidae in that species with numerous stamens have the stamens initiated in centripetal (rather than centrifugal) sequence and usually do not exhibited parietal placentation which is common in Dilleniidae.
Molecular phylogenetic studies indicate that the Rosidae are a natural group only if a large portion of the subclass Hamamelidae and most Dilleniidae are included in it. The Proteaceae should be moved to the "lower hamamelids." The two orders Cornales and Apiales are related to lineages of the Asteridae as suggested by previous morphological and chemical studies.