Ovular morphology and the major classification of the dicotyledons

The distribution within the dicotyledons of the number of integuments and the thickness of the nucellus is reviewed. It is suggested that these characters indicate relationship among major dicotyledonous groups. A unitegmic group with crassinucellate or tenuinucellate ovules is considered ancestral to the main sympetalous complex (Asteridae) and, combined with it, forms one of the major phyletic lines within the dicotyledons. A second group, with bitegmic-tenuinucellate ovules, leads to the Primulales-Ebenales complex.