Diversity and distribution of the genus Asclepias (Apocynaceae: Asclepiadoideae) in Mexico

Asclepias (milkweed) is a genus with 132 species in America, which are distributed from Canada to Argentina. Some of its species are of great importance in the study of biological processes, as well as in traditional and allopathic medicine. However, knowledge about its diversity and distribution in Mexico has not been well documented. The objectives of this work were to analyze the geographic distribution and to evaluate the conservation status of each species occurring in Mexico. A database of 3,195 herbarium records was compiled. Distributions were analyzed using a geographic information system. Species richness was estimated for states, vegetation types, biogeographic provinces and 90 x 90 km grid cells. Asclepias has 75 species in Mexico, of which 34 are endemic. Sonora was the most diverse state with 31 species. Conifer and oak forests, and xerophytic scrub had the highest number of species, 57 and 36 respectively. Among biogeographic provinces, the Chihuahuan Desert had the highest diversity with 45 species. The grid cells with the highest number of species were found in the Transmexican Volcanic Belt and its surroundings, with 20 to 24 species.