Chlorohiptage (Tetrapteroids, Malpighiaceae), a distinct new genus endemic to Vietnam based on morphological and molecular data.

Background and aims – Vietnam is one of the leading diversity centres for Asian Malpighiaceae, comprising 24 accepted species and three native genera (i.e. Aspidopterys, Hiptage, and Tristellateia). During recent fieldwork towards completing the taxonomic revision of Malpighiaceae for the Flora of Vietnam, we have collected specimens from two populations that could not be placed in any of the three native genera of this family. We performed morphological and molecular phylogenetic studies to test the generic placement of those specimens. Material and methods – We sampled 27 genera (including the Asian Acridocarpus, Aspidopterys, Brachylophon, Hiptage, Stigmaphyllon, and Tristellateia, out of a total of 75) of Malpighiaceae representing all phylogenetic clades comprising paleotropical lineages (i.e. acridocarpoids, bunchosioids, tetrapteroids, malpighioids, and stigmaphylloids), the unusual specimen recently collected in Vietnam, and the two genera of Elatinaceae as outgroups. Maximum Likelihood analysis was carried out based on a molecular matrix alignment of the internal transcribed spacer marker (ITS). Comprehensive morphological analyses were also carried out based on the collected specimens and additional herbarium specimens. Key results – Our molecular phylogeny strongly supported the unusual specimen from Vietnam placed as sister to Hiptage in the tetrapteroid clade. Key morphological traits differing these Vietnamese specimens from Hiptage were identified related to the floral bud imbrication, shape, colour, posture of sepals and petals, length of stamen filaments, number of styles, and shape of mericarps, allowing the proposition of a new monospecific genus. Conclusions – Chlorohiptage vietnamensis is proposed as a new monospecific genus closely related to Hiptage but differing in several key morphological traits. A complete morphological description is provided alongside photographic illustrations and notes on its conservation, distribution, ecology, etymology, and taxonomy. Additionally, an updated identification key to the genera of the tetrapteroid clade is provided.