Evolution and biogeography of Malesherbiaceae, an endemic family of arid western South America

Malesherbiaceae, which are endemic to and western South America, provide an interesting research opportunity, as the family's small size and distribution in a virtual continental island make it ideal for phylogenetic and biogeographic studies. The family's distribution in both Chile and Peru is unusual; the adjacent countries share very few desert taxa. Therefore, Malesherbiaceae are an ideal group for the study of the biogeography of the entire dry region west of the Andes.;A phylogeny was reconstructed using ITS sequence data. This analysis confirmed the monophyly of the family and showed it to consist of five major clades. Four of the five major clades contain morphologically similar species; the two species comprising the fifth share few traits. The five major clades are recognized as subgenera.;These subgenera correspond closely to the distributions of species, suggesting that the physical history of the region strongly influenced the evolution of Malesherbiaceae. The morphologically distinct Peruvian species form a terminal clade in the family, indicating Malesherbiaceae originated in Chile and subsequently migrated to Peru. By reference to the region's geological history, it was inferred that Malesherbiaceae split from Turneraceae in the late Miocene. The five subgenera evolved rapidly in the Pliocene, and a more recent radiation event affected much of the family in the Pleistocene.;Allozyme diversities of four Peruvian inter-Andean species were examined. The data suggest that at least two of the species are the result of founder events. Morphological similarities among the four close relatives also suggest a recent divergence. Founder events may be relatively common in the and inter-andean valleys because they are isolated by intervening regions of high elevation.;The M. humilis species complex was also studied in detail because the four species and three varieties previously described are difficult to distinguish. A phenetic analysis of morphological data gathered from herbarium specimens further emphasized the similarities among groups of organisms. Five clusters are recognized as varieties of one species, M. humilis. A former species, M. multiflora, is combined with M. humilis var. parviflora, and two others, M. gabrielae and M. taltalina, are recognized as varieties of M. humilis.