<i>Cestrum amithii</i> (Solanaceae), nueva especie de San Luis Acatlán, Guerrero, México

Background: One specimen collected in Yoloxóchitl (San Luis Acatlán, Guerrero, Mexico) was initially reviewed by Michael Nee, who suggested that it could be a new species of the genus Cestrum, and commissioned to the first author to describe it. Questions: Do Cestrum populations from San Luis Acatlán, Guerrero, correspond to a new species for science? Studied species: Cestrum sp. nov. Study site and dates: Yoloxóchitl, Municipality of San Luis Acatlán, Guerrero; 2023-2024. Methods: The specialized bibliography on the genus Cestrum was examined, from which a list of species with similar morphology to the studied species was compiled, all of which were examined using high resolution digital photographs. A botanical exploration was carried out, locating three populations. A morphological analysis was conducted with the collected material. Results: Cestrum amithii is defined as a new species for science. This new species presents many differences in terms of floral and foliar characters from the other species of the genus. The most outstanding is its spathaceous calyx, which is markedly asymmetrical and large, with evident ribs and two to three lobes. C. amithii is known only from Yoloxóchitl, Guerrero, where it grows in sub-deciduous tropical forest vegetation, at elevations of 530-630 m asl. It is associated with seasonal streams and creeks. Conclusions: With this new discovery, the number of Cestrum species in the flora of Guerrero state increases to 16.