Lecanora exspersa: A new lichen record for North America and a key to sorediate Lecanora (Lecanoraceae) in western North America

Lecanora exspersa Nyl., a corticolous sterile sorediate crustose lichen previously known only from sparse collections in the mountains of Eurasia, is here reported as new to North America. We collected eight specimens attributable to this name as a part of our recently launched comprehensive lichen inventory of the southern Rocky Mountains and adjacent high plains of Colorado. Chemical and morphological study of these specimens as well as a molecular phylogeny containing our specimens, accessions of L. exspersa from Europe, and other sorediate members of the genus with which L. exspersa may be confused, helped to confirm its identification and placement within the L. subfusca group. This new record for North America is characterized by its thin, grey, smooth to verruculose thallus on bark or wood, its discrete, circular mint-green soralia that erupt from verrucae (these becoming larger and plane with age and often bearing a prominent thalline rim), and its production of atranorin and nephrosteranic acid. We provide discussion along with a dichotomous key to help facilitate the identification of this species and other sorediate species of Lecanora from western North America. Continued fieldwork followed by herbarium studies of the Colorado lichen biota will, we predict, yield many new additional records as in the present report as well as species new to science.