CLASSIFICATION OF THE EUPHORBIACEAE

The family Euphorbiaceae appears to be monophyletic, despite proposals for segregate families. The Euphorbiaceae display a great variety of growth forms, including at least 17 ''models'' of Halle. Anatomical characters particularly useful for classification include wood structure, laticifer type, trichomes, and stomata. Inflorescences are basically dichasial, and pseudanthia have evolved several times. Pollen nuclear number and exine structure provide useful criteria for characterizing genera, tribes, and subfamilies. Structure of the seed coat is characteristic for the family and does not provide evidence for a polyphyletic origin of the family. Pollination is prevailingly entomophilous, and seed dispersal by ants is important in many taxa. Geographic distribution patterns of genera show a concentration of primitive taxa in Africa and Madagascar, although in subfamily Crotonoideae there is evidence of a neotropical center. Disjunctions between Africa and South America are common. Bentham's hypothesis of an Old World origin of the family appears well supported. The basic distribution patterns appear to reflect early (Cretaceous and Paleogene) dispersal across land or narrow water barriers and spectacular but rather trivial instances of long-distance dispersal in the late Tertiary and Pleistocene: Tertiary high-latitude dispersals via the Bering land bridge appear to have been relatively insignificant.