Polystemma cualense (Apocynaceae), a new species from western Mexico

A new species of Polystemma is described from the Sierra El Cuale, Jalisco, Mexico. Polystemma cualense is distinguished from its congeners, particularly P. horconesense, by a gynostegial corona higher than the gynostegium, longer external corona lobes, and a black gynostegium. Morphological data were obtained by examining herbarium specimens, consulting digital images from iNaturalist, and reviewing specialized literature.

A preliminary conservation assessment based on IUCN criteria indicates that it is a Critically Endangered (CR) species due to its restricted area of occupancy and threats from deforestation, agriculture, and livestock grazing. The discovery of P. cualense increases the known diversity of Polystemma in Jalisco and highlights the floristic importance of the Sierra El Cuale.