Evolution and biogeography of the Hebe complex (Scrophulariaceae) inferred from ITS sequences

The Hebe complex comprises a putatively monophyletic group distributed from eastern Australia and New Guinea to the Falkland Islands. Analysis of ITS sequences supports five distinct clades within the complex, corresponding to Derwentia plus Hebe formosa, Heliohebe, Chionohebe plus Parahebe trifida, Parahebe, and Hebe. Hebe cheesemanii and Hebe cupressoides form a weakly supported Glade that is distinct from the Hebe Glade. Relationships of Hebe macrantha are poorly resolved. The currently recognised infra-generic classification of Hebe is not supported by this study, and the newly described genus Leonohebe Heads is considered polyphyletic. These results suggest that the progenitor of the Hebe complex originated in Australia. A rapid and extensive radiation followed establishment of a founder population in New Zealand. The combined effects of inbreeding, genetic drift, and strong selection on small populations fragmented by mountain-building and glacia-tion have contributed to its rapid evolution. At least two recent instances of long-distance dispersal between New Zealand and South America are supported.