Usnea rubicunda Stirt.

Nomenclatural data
Scott. Naturalist 6: 104 (1881).—Usnea pensylvanica Motyka, Lich. Gen. Usnea Stud. Monogr., Pars Syst. 2(1): 351 (1937).—Usnea protensa Stirt.—Usnea rubescens Stirt.—Usnea rubrotincta Stirt.—Usnea sublurida Stirt.
Morphology
For a detailed description, see Purvis et al. (1992) and Clerc (2007). Thallus 3–10(–20) cm long, at first erect, later may become longly pendulous; surface reddish brown, more rarely greenish grey with numerous red-brown flecks, especially at the basal part; base not blackened; branches may be segmented but not inflated; fibrils present, few to abundant, arising at right angles from the branches; papillae and tubercles frequent on main branches; soralia punctiform, covered with abundant clustered isidiomorphs. Cortex thick, contains red pigment; medulla compact.
Medullary chemistry
Chemotype (1) with stictic acid (K+ yellow to red, Pd+ orange) as a main substance and norstictic and psoromic acids as accessories; chemotype (2) with salazinic (K+ red, Pd+ orange) acid as a main substance and norstictic acid as an accessory (Purvis et al. 1992).
Remarks
Usually easily recognized due to red-orange or reddish brown thallus colour. However, in some specimens the pigment is sparse or spotty and the basic colour of the thallus is greyish green then (Brodo et al. 2001, James 2003). Numerous isidiomorphs on minute soralia are also characteristic if this taxon.
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Ecology and distribution
Europe (map legend)
Corticolous, on various deciduous trees and, rarely, on conifers, mostly on branches; occasionally on sandstone rocks (Diederich et al. 2008). Grows in ancient woodlands or on isolated trees. Photophilous and hygrophilous, common in areas with an oceanic climate. In Europe it is the most common species in the western part of the continent (Fos & Clerc 2000). Reported in Europe: Albania, Austria, Belgium (probably extinct), Germany, Great Britain, Italy, Luxembourg (probably extinct), Portugal, Slovakia (probably extinct), Slovenia, Spain.