Argyreia Lour. is one of the most taxonomically complex genera of the morning glory family (Convolvulaceae). The number of named species is now 135, and new species are regularly being described. There are several species complexes that are morphologically similar and difficult to tell apart. Therefore, the aim of this study is to explore the species identification criteria for Argyreia, especially new sources for taxonomically informative characters. Ten accessions representing three morphologically similar Argyreia operational taxonomic units (OTUs) were collected and their anatomical characters were investigated using the leaf peeling technique and paraffin sectioning method. Anatomical character states were analyzed using two phenetic analysis methods: clustering analysis (CA) and principal component analysis (PCA). Three distinct clusters were clearly separated in both PCA and CA at the internal similarity coefficient of 0.48 with a high R-value of 0.89757. Nineteen effectively distinguishable character states were derived from the high loadings of the first two components. In conclusion, two of the separated groups were matched with known species, and the third separated group is here delineated as a new species. Therefore, a new species, Argyreia gyrobracteata Traiperm & Chitchak, is described and illustrated together with ecological data and a preliminary conservation assessment.

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This compilation, the first of a series, presents additions, corrections, and amendments to the Convolvulaceae account for the Flora of Thailand that was published 10 years ago. Methods used include the traditional study of dried voucher specimens housed in herbarium collections, field research and collecting, and monitoring photographs of Thai Convolvulaceae shared on selected natural history applications. This initial compilation results in 13 species new to the flora, updates names for eight species, amends taxonomic concepts (and names) for four species, and augments the distribution for 16 species. One orthographic change is made to bring a binomial into conformity with the International Code of Nomenclature. We highlight significant discoveries for two rare and little-known Thai Convolvulaceae species. References are cited to document descriptions, ecology, distributions beyond Thailand, and several new taxonomic works published since 2010.

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