Molecular phylogenetic analysis and taxonomic reconsideration of Ceropegia hirsuta (Apocynaceae, Asclepiadoideae) reveal a novelty in Thailand, Ceropegia citrina sp. nov., with notes on its pollination ecology

Abstract

The identity of Ceropegia hirsuta in Thailand has been questioned. Although this plant is quite similar to the original C. hirsuta from India, being entirely hirsute, with yellowish-shaded flowers, a curved, funnel-shaped corolla tube, and broad corolla lobes shorter than the corolla tube, there are several clear differences in morphological traits between the materials collected in Thailand and the type and further specimens collected in India. Moreover, C. hirsuta s.s. is restricted to Peninsular India. In this study, using molecular phylogenetic analysis based on DNA sequence data for ITS (nuclear) and trnT-L, trnL, and trnL-F (all cpDNA) markers, and classical morphology-based delineation, we demonstrate that the plant from Thailand represents a species on its own clearly separated from C. hirsuta s.s. as well as from all other known congeners. Therefore, we here describe it as a new species, C. citrina, sp. nov. A detailed description, illustrations, and photographs are provided, together with a comparison of morphological traits of C. citrina, C. hirsuta, and another Thai species, C. foetidiflora. We also provide characterization of floral volatile compounds and pollinators. Our study emphasizes that morphological convergence may lead to errors in taxonomic treatment within the genus Ceropegia, and that phylogenetic relationships are largely congruent with geographic distribution.