Two new species of Colletotrichum (Glomerellaceae, Glomerellales) and a new host record for Colletotrichum karsti on Rosa chinensis from southwestern China.

Colletotrichum, a genus of ascomycetous fungi in the family Glomerellaceae, includes many important plant pathogens worldwide. In this study, eight fungal strains collected from plant hosts in southwestern China (Guizhou and Yunnan provinces) were identified as four species of Colletotrichum. Two novel species, Colletotrichum actinidicola and Colletotrichum poalesicola, are described based on morphological characteristics and multilocus (ITS, gapdh, chs-1, act, β-tubulin, his3, and cal) phylogenetic analyses. Phylogenetic analyses placed strains of Colletotrichum fici in a well-supported clade with Colletotrichum boninense, and these taxa are treated as synonyms of Colletotrichum boninense. Similarly, Colletotrichum wuxuhaiense clustered with Colletotrichum karsti and is synonymized with it based on genetic divergence and morphological similarity. Additionally, Colletotrichum karsti isolated from Rosa chinensis (Rosaceae), is introduced as a new host record. One previously known species, Colletotrichum boninense, was also recorded. The integration of molecular and morphological data facilitated accurate species delimitation and improved understanding of Colletotrichum diversity in this region. These findings contribute to the growing body of knowledge on the taxonomy, host associations, and distribution of Colletotrichum species in Asia.