Rediscovery of the Enigmatic Paroxygraphis in Xizang, China: Phylogenetic Evidence for its Reclassification Within Oxygraphis (Ranunculaceae)

Abstract

The enigmatic monotypic genus Paroxygraphis (Ranunculaceae, trib. Ranunculeae), represented solely by P. sikkimensis, has long posed taxonomic uncertainties due to its rarity. Through field rediscovery in southern Xizang province, China, and comprehensive molecular phylogenetic analyses combining nrITS and four plastid regions, we resolve its phylogenetic position within the Oxygraphis clade, with an estimated divergence time of about 3.73 Ma (95% HPD: 1.98-5.77 Ma) from its sister clade. Morphological and ecological characteristics, including 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 trib. Ranunculeae reflects 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 trib. Ranunculeae.