CHROMOSOMAL CYTOLOGY AND EVOLUTION IN EUPATORIEAE (ASTERACEAE)

Reports of 68 new chromosome counts attributed to 53 species from 25 g enera of Eupatorieae of the Asteraceae, based mostly on determinations of mitotic materials, include first counts for 2 genera (Acanthostyle s and Lepidesmia) and 14 species and new reports for 8 species. B chro mosomes are reported for 4 genera and 12 species. Karyotype analyses m ade on 20 species of Eupatorieae and one species of Heliantheae showed that total karyotypic lengths of the taxa with n = 16-19 of heliantho id and eupatorioid taxa are comparable to those of some eupatorioid ta xa with n = 10. This is contrary to the previous hypothesis that the h igher chromosome numbers n = 16-19 were derived from n = 10 by polyplo idization followed by dysploid loss. Cytological data supplement and a re consistent with the following conclusions predicted from molecular phylogenetical and biochemical data: (1) The ultimate base number of E upatorieae is 17, and the lower numbers are derived by successive dysp loid reductions; (2) A reduction in chromosomal and total karyotypic l ength accompanied by evolutionary advancement has been revealed for so me genera and species within this tribe; (3) A high base number of x = 17 in Eupatorieae is considered to be derived directly from one of th e members of Heliantheae with n = 17 to 19.