Centrosema flavescens (Fabaceae, Papilionoideae), a new species from the Yucatan Peninsula, Mexico

Background: Centrosema (Fabaceae) includes 35-44 species in the New World, 10 in Mexico, and 9 in the Yucatan Peninsula. Most species have trifoliolate leaves and bicolored flowers. Unifoliolate leaves are an infrequent character that is found in a few species, e.g., C. sagittatum (Humb. & Bonpl. ex Willd.) Brandegee, but monochromatic flowers, e.g, lacking nectar guides, is even a more unusual character state. Several populations of a Centrosema from the Yucatan Peninsula share both character states, a combination that sets them apart from other members of the genus. Question: Is the Centrosema with unifoliolate leaves, alate petioles, and monochromatic flowers of the Yucatan Peninsula, a species distinct from the phenetically similar C. sagittatum? Studies species: Centrosema (Fabaceae, Papilionoideae). Study site and dates: Yucatan Peninsula, Mexico, 2021-2023. Methods: Botanical specimens were collected and determined taxonomically through the use of relevant literature, keys, and the consulting of botanical collections. The conservation status of the new species was assessed using the IUCN methodology. Results: The specimens collected do represent an undescribed species that differs from Centrosema sagittatum by its smaller, cream-yellow, monochromatic flowers. The species is assessed as Endangered (EN). Conclusions: A new species, Centrosema flavescens from the Yucatan Peninsula is proposed. Eleven species of Centrosema are now recognized in Mexico, nine in the Yucatan Peninsula. C. sagittatum does not occur in the Yucatan peninsula.