Eumitrioid Usnea species (Parmeliaceae, lichenized Ascomycota) in tropical South America and the Galapagos

Eumitrioid Usnea species are characterized by a tubular central axis throughout the entire thallus. Four species were identified in South America: Usnea baileyi is a (sub-) tropical species occurring both in continental South America and the Galapagos; U. perplectata has a scattered distribution worldwide and occurs in continental South America, mainly on the eastern range; U. flaveola and the newly described species U. subflaveola are both so far endemic to the Neotropical Andes. Distinct chemotypes, as well as anatomical characters, such as the thickness ratio of the medulla or the presence of medullar pigmentation, are diagnostic in delimiting these species. A detailed description of the species is provided together with an identification ke