SAXICOLOUS SPECIES OF USNEA SUBGENUS USNEA (LICHENIZED ASCOMYCETES) IN NORTH-AMERICA

Four primarily saxicolous species and eight corticolous, secondarily s axicolous species of Usnea are known In North America. Morphology, che mistry anatomy, ecology, and distribution of the mainly saxicolous Usn ea amblyoclada (Mull. Arg.) Zahlbr. (Syn. nov. U. globularis Motyka). U. ammannii P. Clerc & Herrera-Campos sp. nov., U. halei P. Clerc sp. nov., and U. nashii P. Clerc & Herrera-Campos sp. nov., are described. Usnea ceratina Ach., U. cornuta Koerb., U. dasaea Stirt., U. hesperin a Motyka, U. mutabilis Stirt., U. rubicunda Stirt., U. subscabrosa Mot yka, and U. wirthii P. Clerc are found only occasionally on rocks, and are briefly described. Usnea dasaea, (syn. nov. U. dolosa Motyka, U. galbinifera Asah., U. spinigera Asah., U. spinulifera (Vain.) Motyka, U. undulata Stirt.) is described in detail. Usnea amblyoclada is new f or North America. Usnea dasaea is new for North America, South America , Africa, and Asia. A key for species occurring on rocks in North Amer ica is provided. A new term, fibercles, is proposed for more or less p rotuberant scars left on branches after fibrils have broken.