Lecanora thysanophora R. C. Harris, n. sp. is described. It is a common lic
hen in eastern North America, most often found as a sterile corticolous cru
st, but apothecia are not uncommon when the species grows along streams. Be
sides being recognizable irt the field, it is distinctive chemically: conta
ining usnic acid, zeorin, often porphyrilic acid, and several species-speci
fic terpenoids.