Systematic implications of chloroplast DNA variation in the subtribe Ambrosiinae (Asteraceae: Heliantheae)

The Ambrosiinae is one of the most distinct subtribes of the tribe Heliantheae. Nevertheless, relationships within the subtribe are poorly understood. Chloroplast DNA (cpDNA) restriction site variation was examined in the Ambrosiinae in order to determine the phylogenetic relationships of the genera within the subtribe; the DNA findings are compared with chemical, morphological, and cytological data. The cladograms constructed from the molecular data recognized two groupings in the Ambrosiinae: one includes Parthenium, and the other includes the rest of the genera. In the latter, two major clades were suggested: 1) Iva s. str. and Parthenice; and 2) Ambrosia s.l., Dicoria, Euphrosyne, Xanthium, and Cyclachaena of Iva. The cpDNA results further indicate that several genera as presently circumscribed, such as Iva s.l., Ambrosia s.l. and Hymenoclea are paraphyletic. Moreover, the genus Iva s.l., including the five small genera Oxytenia, Leuciva, Chorisiva, Cyclachaena, and Iva s. str., consists of two well-differentiated lineages. Parthenice and Parthenium both appear to belong within the Ambrosiinae