Extensive yellow crusts below limestone overhangs: a new taxon close to a minute epiphytic lichen

A conspicuous yellow crust forming extensive covers on some dry and shaded limestone rocks in Europe is described here as Caloplaca substerilis subsp. orbicularis M. Haji Moniri, Vondrák & Malíček subsp. nov. Based on nuITS rDNA, 28S nuLSU rDNA and mtSSU rDNA sequence data, the new taxon is closely related to Caloplaca substerilis and C. ulcerosa . The three taxa form a supported clade in the subfamily Xanthorioideae (Teloschistaceae), but none of the recently seggregated genera are suitable for them. In the ITS phylogeny, the new taxon forms a monophylum nested within C. substerilis . However, its extensive yellow thalli and absence of vegetative diaspores clearly distinguish it from Caloplaca substerilis (subsp. substerilis ). Indeed, if it had not been for the molecular evidence, we would have described it at the rank of species. We suggest that the substrate switch and accompanying processes are responsible for the striking phenotypic difference between Caloplaca substerilis subsp. substerilis and C. substerilis subsp. orbicularis .