Ruehssia golfomexicana (Apocynaceae; Asclepiadoideae), a new species from Mexico and Central America

Background: Ruehssia is the only genus of Marsdenieae occurring in the Americas, and is restricted to this region with around 150 species. Mexico and Brazil have been recognized as the principal centers of diversity of the genus. The distinctive morphology and localities of the collected plants in Veracruz and Campeche, Mexico, suggests that this is a new species. Questions: Do the collected specimens belong to a new species? What is its conservation status? Studied species: Ruehssia golfomexicana. Study site and dates: Mexico and Central America, 2024-2025. Methods: Botanical specimens were analyzed and compared with a literature review, herbarium specimens, and photographic records from iNaturalistMX. The conservation status of the new taxon was evaluated, following the International Union for Conservation of Nature Red List criteria. Results: Ruehssia golfomexicana is compared with R. propinqua, R. hiriartiana, R. veronicae, and R. zimapanica. The proposed new species differs by its glabrous leaves, numbers of inflorescences per node and the green to greenish-yellow flowers, the new taxon is categorized as Endangered. Conclusions: Ruehssia is a genus of significant diversity in Mexico, and with this new addition reaches 42 species. This diversity places it as the third most species-rich genus of Apocynaceae in Mexico.