Occurs in lichens. Isoln from Lecanora sordida (Pers.) Th. Fries, Parmeliaceae: Hesse, J. Prakt. Chem. 58, 497 (1898); Kennedy et al., Sci. Proc. R. Dublin Soc. 21, 557 (1937); from Roccella montagnei, Graphidaceae: Subbaraya, Seshadri, Proc. Indian Acad. Sci. 12A, 466 (1940); from Crocynia membranacae (Dicks.) Zahlbr., Chrysotrichaceae: Akermark et al., Acta Chem. Scand. 13, 1855 (1959). Structure: Kennedy et al., loc. cit. Absolute configuration: Akermark, Acta Chem. Scand. 16, 599 (1962).