PHYLOGENY AND DISJUNCT DISTRIBUTION - EVOLUTION OF SAINTPAULIA (GESNERIACEAE)

The molecular phylogeny of African violets (Saintpaulia H. Wendl.); ba sed on ribosomal DNA internal transcribed spacer (ITS) sequences; foll ows the disjunct biogeography of the genus. Sequence analysis by parsi mony of 19 accessions, representing 17 currently recognized Saintpauli a species, resulted in four trees of 182 steps. The first major divisi on is between S. goetzeana, from the Uluguru Mts, Tanzania, and the re st of the genus. The basal position of S. goetzeana, and its putative primitive characters, may indicate an Uluguru origin for Saintpaulia a nd subsequent colonization of the more northerly mountains. Of the rem ainder, S. teitensis, from the Teita Hills of Kenya, is sister taxon t o the other species (which occur mainly in the Usambara Mts of north-e ast Tanzania). A group of nine Usambaran species that we call the 'ion antha complex' show minimal ITS genetic differentiation and are also t axonomically critical. Species diversity in the Usambara Mts appears t o be the result of rapid, recent (possibly Pleistocene) radiation. Thi s study reveals the limitations of ITS sequences for elucidating the r adiation of poorly differentiated species (the ionantha complex). Howe ver, the molecular data strongly suggest that conservation of the Ulug uru and Teita populations is essential for the protection of the full range of diversity within the genus.