Two new Lactarius species from Laos (Basidiomycota, Russulales)

Two new species of milkcaps, Lactarius megaplinthogalus and L. rosascens, are described from montane forests in Xieng Khouang Province, northern Laos, Southeast Asia. Both species were collected in mixed forests dominated by Fagaceae and Pinaceae and are documented using detailed macro- and micromorphological observations in combination with ITS rDNA sequence data. Lactarius megaplinthogalus is distinguished by its large, stout, dark brown to blackish basidiocarps, very distant lamellae, sticky white latex that stains the lamellae pinkish to blackish, and thick-walled basidia. Lactarius rosascens is recognized by its yellow to honey-colored, scrobiculate pileus, abundant white latex rapidly turning bright pink to wine-red and intensely staining the lamellae, and a well-developed trichodermal pileipellis. Phylogenetic analyses support their recognition as distinct species and place the first species in L. subg. Plinthogalus (section Plinthogalus) and the latter one in L. subg. Lactarius (unclassified at the sectional level). These findings highlight the exceptional and still underexplored diversity of milkcaps in Laos (and more generally in Southeast Asia) and underline the importance of continued mycological surveys and integrative taxonomic approaches in the region.