A NEW SPECIES OF SEDUM SECTION PACHYSEDUM (CRASSULACEAE) AND A DIVERSITY ANALYSIS OF THE GENUS IN THE SIERRA MADRE OCCIDENTAL, MEXICO

Background: The Mexican Transition Zone represents a center of diversification and an endemism area for Sedum subgenus Sedum. The Sierra Madre del Sur, Mexican Volcanic Belt, Sierra Madre Oriental and Sierra Madre Occidental (SMO) biogeographic provinces contain the highest diversity of the subgenus. The SMO stands out for the endemism of Sedum, that is why additional exploration and study of the group in the area could contribute to the discovery of new species. Question: Could the critical analysis of the morphology of Sedum individuals found in recent explorations in the SMO show the existence of undescribed species? Studied species: The genus Sedum species. Study site and dates: Sierra Madre Occidental, Mexico, during the years 2019-2021. Methods: Several botanical explorations and collections of Sedum were carried out in Durango and Sinaloa. The collected materials were subjected to critical analysis of their morphology to prepare descriptions and comparative tables contrasting morphologically related species. Records of Sedum were obtained, verified, and analyzed to prepare distribution maps in the SMO. Results: Sedum acaxee is proposed as a new species of section Pachysedum. The description is accompanied by photographs, a comparative morphology table, and a list and maps of Sedum in SMO. Conclusions: The high proportion of type localities (26 spp.) and endemism (23 spp.) of Sedum for the SMO highlight the high diversity of the genus in the province and shows the need to continue with botanical explorations in this mountainous complex.