Molecular phylogeny of Eupatorieae (Asteraceae) estimated from cpDNA RFLP and its implication for the polyploid origin hypothesis of the tribe

The tribe Eupatorieae has a chromosome base number that ranges from 4 to 25 . A molecular phylogenetic analysis using cpDNA restriction site mutations was performed. Fifteen species representing 13 subtribes of the tribe Eupat orieae were examined, together with three species from the tribe Helianthea e as outgroups. A total of 103 restriction site mutations were detected, an d 31 of these were phylogenetically informative. Parsimony analysis produce d a single most parsimonious tree with 117 steps. This tree suggested that two clades diverged early in the evolution of the tribe Eupatorieae. One cl ade includes Neomirandea (x=17 and 25), Ageratina (x=17) and Sclerolepis (x =15) with the higher chromosome base numbers, and the other includes Mikani a (x=17) and the remaining genera with lower chromosome base numbers (x=10- 11). However, the monophyly of the former clade is supported with a low boo tstrap value. In the latter clade, Mikania (x= 17) diverged first, then Ste via (x=11), and finally eight genera with x=10 diverged in succession. This result supports the hypothesis that the genera in the tribe Eupatorieae wi th x=10 evolved from an ancestor with a higher base number, and the tribe i s of polyploid origin.