Themes > Science > Botanical Sciences > Classification of Plants > Spermatophyta (Seed Plants) > Angiosperms (flowering Plants) > The Rosidae


The Subclass Dilleniidae, includes 18 orders, 116 families and over 60,000 species.  The largest subclass with regard to number of families and more or less tied with the Asteridae with regard to species divrsity.  As was the case with the Dilleniidae, about 75% of the species occur in five orders; in this case the Fabales (18,000), Myrtales (9,000), Euphorbiales (8,000), Rosales (6,600) and Sapindales (5,400).
 
 

A diverse set of flowering plant orders that, like the Dilleniidae, lacks a distinct set of key characters.  General trends or features of the Subclass include:

  • syncarpy is the rule, with the exception of the high frequency of apocarpy in the Rosales and monocarpy in the Fabales and Proteales.
  • Leaves are often simple or, if compound, often pinnately compound
  • petals usually distinct, sometimes wanting, sometimes connate at the base, rarely sympetalous.
  • nectary disks of various types are frequently encountered, many stamodial in origin and positioned at the base of the ovary.
  • placentation  is various, but most often axile with, generally, fewer ovules per locule than found in the Dilleniidae.
Cronquist: "In the last analysis, the Rosidae and Dilleniidae are kept apart as subclasses because each seems to constitute a natural group separately derived from the ancentral Magnoliidae, rather than because of any definitive distinguishing characters...it is conceptually more useful to hold the two as separate subclasses than to combine them into one or to abandon any attempt at organization of the Magnoliopsida into subclasses."  THEREFORE:  Focus here is on distinctive characters at the order and family level.


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