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Species of the foliose genus Xanthoparmelia (Ascomycotina: Parmeliaceae) are among the most abundant lichens occurring on rocks and soil throughout arid and semi-arid regions of South America stretching from Tierra del Fuego to the northeast portion of Brazil and along the Andean Cordillera. They are found in wide range of open habitats from sea level to well over 4000 m. Their typical light green or yellow green color, due to the presence of usnic acid in the upper cortex, and rhizinate lower surface provide a simple means to recognize the genus, but these characters in themselves do not adequately circumscribe Xanthoparmelia. To fully characterize a specimen cell wall polysaccharides and, where appropriate, apothecial characters must be considered.