Rediscovery of the Enigmatic Paroxygraphis in Xizang, China: Phylogenetic Evidence for Its Reclassification Within...

The enigmatic monotypic genus Paroxygraphis (Ranunculaceae, tribe Ranunculeae), represented solely by P. sikkimensis, has long posed taxonomic uncertainties due to its rarity. Through field rediscovery in southern Xizang, China, and comprehensive molecular phylogenetic analyses combining nrITS and four plastid regions, we resolved its phylogenetic position within the Oxygraphis clade. We found the Oxygraphis clade has a divergence time of about 19.26 Ma (95% HPD: 11.84-27.14 Ma) from its sister clade, and Paroxygraphis is nested within. Morphological and ecological characteristics, including a small herb with a rosette of basal simple leaves, longitudinally ribbed achenes, and its alpine adaptations, further support this relationship. Furthermore, the results showed that persistent sepals and unisexual flowers in Ranunculeae reflect multiple independent evolutionary origins. We propose the new combination Oxygraphis sikkimensis and highlight its critically endangered status due to habitat vulnerability. Lectotypification of P. sikkimensis is also made. This study provides new data for the floristic research of China and resolves the long-standing taxonomic controversy of this problematic genus within Ranunculeae.