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

During scientific expeditions across the Qinghai-Tibetan Plateau, a group of <i>Buellia</i> 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 (<i>rpb2</i>), and β-tubulin gene (<i>tubb</i>). Three species, which formed a new distinct lineage within <i>Buellia</i> s.l. were confirmed as new to science: <i>Buellia plana, B. elevata</i>, and <i>B. tibetana</i>. This lineage is here referred to as the <i>pruinocalcarea</i>-group because of a species previously described that belongs to this group: <i>B. pruinocalcarea</i>. Species included in this group are closely related to <i>Tetramelas</i>; the group also has affinities to the <i>epigaea</i>-group and <i>subalbula</i>-group. Detailed descriptions, photographs of the new species, and a key to the species are provided.