Pacific Biogeography of the Asteraceae Genus Abrotanella (Senecioneae, Blennospermatinae)

Abstract

Historical biogeography of the trans-Pacific Asteraceae genus Abrotanella (Senecioneae, Blen- nospermatinae) was analyzed with cladistic methods. The genus comprises 19 alpine species and is restricted to six areas of endemism, South America, Australia-New Guinea, Tasmania, New Zealand, Stewart Island, and the sub-Antarctic Campbell and Auckland Islands. Two area cladograms were constructed, one conform- ing to the sequence of Gondwanaland break-up, the other considering also the physical barrier of a glaciated Antarctica. Four fully resolved cladograms of Abrotanella were mapped on the area cladograms using the computer software COMPONENT to assess conformity between distribution patterns in Abrotanella and geological area relationships. The analysis revealed a convoluted pattern, suggesting several cases of dispersal. The distribution of the species apparently reflects migration, possibly via stepping stones along former archipelagos, and long-distance dispersals. A possible ancestral area was estimated by the use of ancestral area analysis, reversible parsimony, and Fitch optimization. All methods indicate South America as part of the area where Abrotanella originated. The distribution of at least two species are most parsimoniously explained by dispersals from South America to Stewart Island and from New Zealand to Australia and New Guinea, respectively. Removal of these two allegedly dispersed species from the component analyses reveals an underlying pattem in agreement with geology if South America is considered as the sister area to the West Pacific.