SYSTEMATIC IMPLICATIONS OF CHLOROPLAST DNA VARIATION IN THE SUBTRIBE AMBROSIINAE (ASTERACEAE, HELIANTHEAE)

The Ambrosiinae is one of the most distinct subtribes of the tribe Hel iantheae. Nevertheless, relationships within the subtribe are poorly u nderstood. Chloroplast DNA (cpDNA) restriction site variation was exam ined in the Ambrosiinae in order to determine the phylogenetic relatio nships of the genera within the subtribe; the DNA findings are compare d with chemical, morphological, and cytological data. The cladograms c onstructed from the molecular data recognized two groupings in the Amb rosiinae: 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. 1., Dicoria, Euphrosyne, Xanth ium, and Cyclachaena of Iva. The cpDNA results further indicate that s everal genera as presently circumscribed, such as Iva s. 1., Ambrosia s. 1, and Hymenoclea are paraphyletic. Moreover, the genus Iva s. 1., including the five small genera Oxytenia, Leuciva, Chorisiva, Cyclacha ena, and Tva s. str., consists of two well-differentiated lineages. Pa rthenice and Parthenium both appear to belong within the Ambrosiinae.