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 ch aracters 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 charac teristic for the family and does not provide evidence for a polyphylet ic origin of the family. Pollination is prevailingly entomophilous, an d seed dispersal by ants is important in many taxa. Geographic distrib ution patterns of genera show a concentration of primitive taxa in Afr ica and Madagascar, although in subfamily Crotonoideae there is eviden ce of a neotropical center. Disjunctions between Africa and South Amer ica are common. Bentham's hypothesis of an Old World origin of the fam ily appears well supported. The basic distribution patterns appear to reflect early (Cretaceous and Paleogene) dispersal across land or narr ow water barriers and spectacular but rather trivial instances of long -distance dispersal in the late Tertiary and Pleistocene: Tertiary hig h-latitude dispersals via the Bering land bridge appear to have been r elatively insignificant.