Another remarkable new species of Dictyanthus (Apocynaceae, Asclepiadoideae, Asclepiadeae, Gonolobinae) with a long stylar head from Mexico

Dictyanthus includes 17 climbing species distributed from northern Mexico to Nicaragua. Mexico is its main center of diversification with 15 endemic species. The genus is known for its conspicuous flowers with high ornamental potential. Dictyanthus species are distinguished by the shape of their corolla (campanulate or rotated), their pattern of color lines or reticulations on the corolla lobes, the size and shape of their corona, and the shape of the stylar head. The present work formally names as a new species, and describes and illustrates the plants with a long and conspicuous stylar head, distinguishing it from the rest of its relatives. The study consisted of field work for two years, as well as a review of herbarium material and literature. The description of the organism was based on in situ morphology, herbarium material and specimens preserved in ethanol. The conservation assessment was based on IUCN criteria. We follow the cohesive species concept as an explanatory hypothesis for the taxa. A dichotomous key and comparative plates are presented for species with stylar head projection. Dictyanthus unicornus differs from other species in the genus by its conspicuously elongated stylar head and the combination of patent corolla lobes and fleshy, spatulate crown lobes protruding from the corolla throat. According to IUCN criteria, this species is considered Endangered. With the present discovery, the genus Dictyanthus reaches 18 described species of which 16 endemic to Mexico.