Diversity and taxonomy of Phragmidium on Rosa in China, with descriptions of two new species.

The rust genus Phragmidium (Phragmidiaceae, Pucciniales) comprises significant plant pathogens infecting Rosaceae, particularly species of Rosa. Although numerous Phragmidium taxa have been recorded on Rosa in China, their evolutionary relationships and true species diversity remain poorly resolved. Here, a systematic summary of Chinese Rosa-associated Phragmidium is presented by integrating detailed morphological examinations with multilocus phylogenetic analyses of ITS and LSU sequence data, using extensive specimens deposited in major international fungaria and herbaria. Two novel species, P. shennongjiaense and P. xinjiangense, are described and illustrated, and the phylogenetic affinities of 21 previously accepted species are clarified based on updated taxonomic accounts. This work underscores the indispensability of an integrative taxonomic framework-coupling morphological nuances with multilocus datasets-for accurately delineating species boundaries and resolving the rich cryptic diversity of rust fungi in East Asia.