The classification of dicotyledons: A study of the upper levels of the hierarchy

Abstract

Data on 83 attributes were compiled for a sample of 543 genera of dicotyledons. Computational analyses and subsequent consideration suggest that a useful distinction can be made between crassinucellate (mainly apetalous and polypetalous) and tenuinucellate (mainly sympetalous) genera. The crassinucellate series incorporates rather distinct caryophylloid and magnolioid assemblages, the former corresponding to a large extent with the Caryophyllidae of recent taxonomic schemes, the latter being a greatly extended version of the Magnoliidae. No evidence is found to support the Rosidae or Dilleniidae as taxonomic groupings. The tenuinucellate series seems to include two previously unrecognized major groups, here called acanthoids and asclepioids, plus Compositae and Umbelliferae as outliers. The large orders Rosales, Umbellales, and Myrtales may well be taxonomically unsound.

The shortage and general inaccessibility of truly comparative data constitutes a serious difficulty in considering major taxonomic problems; in general these demand better information than seems currently obtainable if reliable results are to be obtained.