ALLOZYME DIVERGENCE AMONG SPECIES OF WOLFFIA (LEMNACEAE)

The genus Wolffia was surveyed electrophoretically at 14 allozyme loci . A total of 133 clones representing 10 of the 11 recognized species w as examined. Genetic identities among most pairs of species are zero, with non-zero values ranging from 0.14 to 0.40. Wolffia angusta and th e newly described W. neglecta show the highest similarity, and the for mer species has an identity of 0.14 with W. australiana. The next high est similarity (0.34) occurs between W. globosa of Southeast Asia and W. cylindracea of southern Africa, which until recently, had generally been viewed as members of the same species. Other species showing som e common alleles are members of a complex involving W. arrhiza, W. col umbiana, W. cylindracea, and W. globosa. Within W. arrhiza, plants fro m South Africa and Europe are easily distinguished electrophoretically because each contains unique alleles at two loci. Strains from other parts of Africa vary at these loci and are not totally distinct from e ither the plants from South Africa or from Europe. Species of Wolffia are much more divergent at allozyme loci than the majority of congener s of flowering plants. This suggests that the species are quite old an d that the difficulties in distinguishing taxa morphologically are the result of reduction rather than lack of divergence due to recent spec iation. Because of the lack of shared alleles between the majority of species pairs in Wolffia, enzyme electrophoresis provides limited reso lution of species relationships in the genus.