Phylogenetic and Biogeographic Aspects of Sophora Sect. Edwardsia (Papilionaceae)

Abstract

Sophora comprises 45-50 species of worldwide distribution, but no general proposal as to the evolution of this group has been put forth. We used cladistic relationships of the quinolizidine alkaloids (matrine, sparteine, methylcytisine, anagyrine, and sophoranol) with morphological and palynological characters to suggest a hypothesis of evolutionary and biogeographic relationships. The mainland Chilean species of Sophora appear to have been derived from' ancestors phylogenetically near the extant Argentinean species S. linearifolia and S. rhynchocarpa and the psammophyte S. tomentosa, growing at tropical coastal sites around the world. The Boreotropic hypothesis of Lavin and Luckow is incorporated in our model as the most parsimonious explanation of the evolution of the species of Edwardsia. Sophora is a taxonomic group that meets the following criteria: a center of diversity in North America, an early Tertiary record in North America, and a pantropical distribution. Styphnolobium and Sophora (including Calia) are representatives of Sophora s.l. in the United States, suggesting a migration of the latter from the Northern Hemisphere to South America. Consistent with the Boreotropic hypothesis, a primary diversification center in South America and subsequent migration to the Indian Ocean and New Zealand, the Juan Fernandez Archipelago, Easter Island, and possibly the Hawaiian Islands is the simplest explanation for the evolution of the Edwardsia species.