A revision of the usnic acid containing taxa belonging to Lecanora sensu stricto (Lecanorales: Lichenized ascomycotina)

Eighteen taxa belonging to the Lecanora subfusca group that contain usnic acid in addition to atranorin are revised on a worldwide basis. The following species are described as new: L. alba Lumbsch from Australia, L. floridula Lumbsch from Florida, L. formosula Lumbsch from Australasia, L. neonashii Lumbsch from Mexico, and L. transvaalensis Lumbsch from South Africa. A xanthone containing population of L. wilsonii is distinguished as L. wilsonii ssp. xanthophora Lumbsch. Lecanora achroella and L. subflavicans are reduced to synonymy with L. achroa, and L. elatinoides var. straminea with L. elatinoides. A key to the taxa treated is included. After consideration of the morphological, anatomical, and chemical variation, it is concluded that the usnic acid containing species of Lecanora do not form a natural group and cannot be separated from Lecanora s. str.