CHLOROPLAST DNA VARIATIONS IN SECT - CYCLACHAENA OF IVA (ASTERACEAE)

Much argument has been occasioned by questions having to do with gener ic concepts in the tribe Heliantheae, subtribe Ambrosiinae, especially involving the genus Iva. Some workers recognize five genera (e.g., Le uciva, Chorisiva, Oxytenia, Cyclachaena, and Iva s. str.), while other s recognize only a single genus Iva s. 1. Although chemical, pollen ul trastructure, and other morphological data have challenged the latter concept, relationships among the segregate taxa are still unclear. The current study used cladistic analyses of chloroplast DNA variation to investigate evolutionary relationships within Iva s. 1., especially w ithin the controversial section Cyclachaena. Nuclear rDNA was also uti lized to test for hybrid origin of selected taxa. The results support the dismemberment of Iva s. 1. and recognition of Iva s. str., largely because Iva s. 1. is shown to be paraphyletic. Most members of the se ction Cyclachaena were found to have relatively close interspecific re lationships. Nevertheless, cpDNA data strongly support two lineages wi thin Cyclachaena. One lineage, including I. xanthifolia, I, acerosa, I , nevadensis, and I. dealbata, has a close relationship with the genus Euphrosyne. The second lineage includes only one species, I. ambrosia efolia, which is closely related to Dicoria. The origin of I. ambrosia efolia was shown to be monophyletic, not involving hybridization.