EVOLUTION OF ERIGERON (COMPOSITAE) IN THE JUAN FERNANDEZ ISLANDS, CHILE

Six endemic species of Erigeron occur in the Juan Fernandez Islands: E. fernandezianus, E. ingae, E. luteoviridis, E. rupicola, E. stuessyi, and E. turricola. The last five are restricted to the younger and more distant island, Masafuera (1-2 million years old), and E. fernandezianus occurs on Masafuera and Masatierra (ca. 4 million years old). All species have n = 27. Phenetic analysis suggests that all six species have come from a single introduction from southern South America, perhaps coastal southern Peru or central Chile. Cladistic analysis reveals two major clades: one involving E. rupicola and E. stuessyi, and the other containing the other four species. In the latter line, E. ingae and E. turricola form a closely related paraphyletic species pair, and E. luteoviridis and E. fernandezianus represent a closely allied holophyletic unit. Phytogeographically, the genus apparently became established first on Masafuera, with subsequent (and more recent) colonization of Masatierra. Speciation appears to have followed a pattern of adaptive radiation with discernible geographic and ecological isolation. Flavonoid compounds from 56 populations of endemic species in the archipelago and from 10 populations of five species on the continent exhibit interpopulational variation, which compromises the value of flavonoids for systematic purposes. Erigeron rupicola and E. stuessyi have similar profiles that differ from the other species.