ABSTRACT: A floristic study of the yellow cetrarioid lichens containing usnic acid (fam. Parmeliaceae, lichenized Ascomycota) which are found in Tibet and neighbouring areas is presented. Typical characters, chemical constituents and distribution data are reported for all 26 species from seven genera (Allocetraria, Cetraria, Cetreliopsis, Flavocetraria, Nephromopsis, Tuckneraria and Vulpicida). Complete descirptions are provided for several taxa which have not been included in recent reviews of the cetrarioid genera. Two identification keys for taxa - both at generic and species level - have been compiled. Worldwide distribution maps are presented for the first time for some Allocetraria, Cetraria, Cetreliopsis and Tuckneraria species.

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