The Argyreia collinsiae species complex (Convolvulaceae): phenetic analysis and geographic distribution reveal subspecies new to science.

Argyreia Lour. is a speciose genus in the Convolvulaceae. However, the genus contains several problematic species complexes due to their morphological similarity. In this study, we aimed to resolve the Argyreia collinsiae complex, which consists of four similar operational taxonomic units (OTUs), i.e., A. collinsiae (Craib) Na Songkhla & Traiperm, A. dokmaihom Traiperm & Staples, A. versicolor (Kerr) Staples & Traiperm, and a peculiar OTU typically known as the large-bract morphotype of A. collinsiae. Following morphological comparison and phenetic analysis, all four OTUs were found to be distinct. However, the large-bract morphotype of A. collinsiae was confirmed to be more closely related to the original morphotype of A. collinsiae than to the other two species. Species distribution modeling (SDM) was then conducted for both morphotypes of A. collinsiae, revealing different geographical ranges of suitable habitat for each. In conclusion, the large-bract morphotype of A. collinsiae was described in this study as a new subspecies, A. collinsiae subsp. megabracteata Traiperm & Srisombat, subsp. nov., based on morphological differences and separate geographic range. We also provide here an identification key, description, detailed illustrations, distribution data, and ecological notes of the new subspecies. An updated description of A. versicolor and an assessment of its conservation status were also prepared since the original description was based solely on dried herbarium specimens and lacks key details.