Molecular phylogenetic and morphological analyses support recognition of a new species of Vincetoxicum (Apocynaceae, Asclepiadoideae) from eastern Thailand

Abstract

An unknown Vincetoxicum species has recently been discovered in northeastern Thailand. It is a twiner that resembles in its morphology and ecology V. flexuosum var. flexuosum, a variable species widely occurring from tropical Asia to Australia. Comprehensive morphological examination showed that despite similarities in growth habit, leaf shape, branching of the inflorescence and flower colour, these two taxa exhibit substantial differences in both vegetative and reproductive traits that clearly distinguish one from the other, particularly shape of the flower bud and indumentum on the corolla lobes. In addition, we also evaluated phylogenetic relationships based on DNA sequence data for ITS, trnT-L, trnL, and trnL-F markers of this new Vincetoxicum sp. with congeners (including, inter alia, new sequences of V. flexuosum var. flexuosum and also those of V. flexuosum var. tenuis, the other variety occurring in Thailand). The analyses demonstrated that the new Vincetoxicum sp. is not closely related to the taxa recognized as V. flexuosum. The new species was instead retrieved as sister to a clade containing the African taxa, V. caffrum, V. lycioides and V. fleckii. Therefore, integrated analyses of morphology and molecular phylogeny revealed Vincetoxicum sp. to be a well-defined species clearly distinct from V. flexuosum, as well as from all other known congeners. The morphological similarity between the new Vincetoxicum sp. and V. flexuosum var. flexuosum likely resulted from convergence, leading to various taxonomic complications. We here describe it as a new species, V. sangyojarniae, sp. nov., and provide a detailed description, illustration, photographs, and comparison to the morphologically similar V. flexuosum var. flexuosum. A preliminary taxonomic reconsideration of the infraspecific taxa under V. flexuosum is also suggested.

Specialized pollination by cecidomyiid flies and associated floral traits in Vincetoxicum sangyojarniae (Apocynaceae, Asclepiadoideae)

“…Vincetoxicum sangyojarniae is a slender twiner recently described from Thailand (Kidyoo & Kidyoo 2023). It has ovate to oblong‐lanceolate leaves, and 20–many‐flowered branched cymes with one to four zigzag rachises.…”

“…During fieldwork in eastern Thailand, we had the opportunity to investigate pollination ecology of the climbing species Vincetoxicum sangyojarniae (Kidyoo et al . 2023; Kidyoo & Kidyoo 2023), found in a protected area within the Rajamangala University of Technology Isan Surin campus, Surin Province. Individuals of this species have also been cultivated in an open garden in Bangkok Province, central Thailand, outside the plant's native range, and comparative studies in the two localities were conducted.…”