Three new species of Buellia s.l. from the Qinghai-Tibetan Plateau represent a new lineage, the pruinocalcarea-group

During scientific expeditions across the Qinghai-Tibetan Plateau, a group of Buellia species were frequently collected from alpine arid regions. These were characterized by having whitish chalky thalli, a surface covered with thick coarse pruina, a reddish-brown hypothecium, and the presence of xanthones. Detailed observations were made of specimen morphology and anatomy. Phylogenetic analysis was conducted based on four loci: the internal transcribed spacer of the rDNA (ITS), partial large subunit nuc rDNA region (28S), RNA polymerase II second largest subunit gene (rpb2), and β-tubulin gene (tubb). Three species, which formed a new distinct lineage within Buellia s.l. were confirmed as new to science: Buellia plana, B. elevata, and B. tibetana. This lineage is here referred to as the pruinocalcarea-group because of a species previously described that belongs to this group: B. pruinocalcarea. Species included in this group are closely related to Tetramelas; the group also has affinities to the epigaea-group and subalbula-group. Detailed descriptions, photographs of the new species, and a key to the species are provided.