Abstract

Eight primarily saxicolous Usnea subgenus Usnea species are reported from Argentina and Uruguay: U. amblyoclada Arg.) Zahlbr. (syn. nov. U. pinnata Rasanen), U. densirostra Motyka, U. durietzii Motyka (syn. nov. U. caespitia Motyka), U. exigua J.M. Rodr. P. Clerc sp. nov., U. fastuosa (Mull. Arg.) Zahlbr., U. hieronymii Kremp. (syn. nov. U. hieronymii var. adusta Kremp.), U. lutii J.M. Rodr. P. Clerc sp. nov. and Usnea saxidilatata J.M. Rodr. P. Clerc sp. nov. are described with morphological, anatomical and chemical data. Their taxonomy and distribution are discussed. A key to the saxicolous species, including those occurring secondarily on rocks (i.e., U. columbiana Motyka, U. cornuta Korb., U. dasaea Stirt. and U. cf. perhispidella J. Steiner) is provided.