Usnea mutabilis Stirt.

Nomenclatural data
Scott. Naturalist 6: 107 (1881).—Usnea marocana Motyka, Lich. Gen. Usnea Stud. Monogr., Pars Syst. 2(1): 359 (1937).
For a detailed description, see Clerc (1994, 2007) and Clerc & Herrera-Campos (1997). Thallus shrubby to subpendent; base pale or brownish; fibrils present, sparse; papillae absent; soralia punctiform, flat or slightly tubercular; isidiomorphs numerous. Cortex thin, glossy; medulla thin, dense, wine red.
Medullary chemistry
Chemotype (1) with fatty acids of the murolic acid complex (K–, Pd–) as main compounds (Fos & Clerc 2000) is known in Europe; chemotype (2) with eumitrin A2 as a main compound and fatty acids of the murolic acid complex and norstictic acid as accessories were recently reported from North America, Sonoran region (Clerc 2007).
Morphologically and chemically closely related to Usnea hirta (Fos & Clerc 2000).
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Ecology and distribution
Europe (map legend)
Mainly corticolous, rarely saxicolous (Clerc & Herrera-Campos 1997), prefers humid sites. In Europe it is present in the Mediterranean region only (Fos & Clerc 2000). Reported in Europe: France, Italy, Portugal, Spain.