Usnea cornuta Körb.

Nomenclatural data
Parerga lichenologica, p. 2, Breslau (1865).—Usnea confusa Asahina, Lich. Jap. 3: 97 (1956).—Usnea inflata Delise ex Duby, Botanicon Gallicum 2: 615 (1830), nom. nud.—Usnea inflata (Duby) Motyka, Lich. Gen. Usnea Stud. Monogr., Pars Syst. 2(1): 510 (1937).—Usnea intexta Stirt.
Morphology
For a detailed description, see Clerc (1987b, 2007) and Purvis et al. (1992). Thallus clearly shrubby, 2–6(–10) cm; main branches inflated, secondary branches distinctly constricted at their base, secondary branches often curved; base concolorous to the branches or light brown; fibrils present, short, often numerous on the tips; papillae few to numerous; soralia (and isidiomorphs) are concentrated at branch tips (including fibrils), becoming confluent, while young soralia are punctiform; isidiomorphs are numerous at the beginning, but often eroded on old soralia. Cortex glossy, thin; medulla thick and loose.
Medullary chemistry
Two chemotypes have been recorded by Clerc (1987b) and Purvis et al. (1992) from Europe: (1) chemotype with salazinic acid as a main substance (K+ red, Pd+ yellow to orange) and protocetraric acid as an accessory; (2) chemotype with stictic and norstictic acids as main substances (K+ yellow to orange, Pd+ yellow to orange) and salacinic acid as an accessory. Further chemotypes are reported from North America, Sonoran region by Clerc (2007): (3) chemotype with lobaric and norstictic acids as main substances; (4) chemotype with norstictic acid alone as a main substance; (5) chemotype with protocetraric acid alone as a main substance; (6) chemotype with no medullary compounds. Various substances (e.g. consalazinic, constictic, cryptostictic, menegazziaic acids or fatty acids) may additionally occur as minor accessories in different chemotypes.
Remarks
Belongs to the U. fragilescens aggregate. Morphologically a highly variable taxon.
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Ecology and distribution
Europe (map legend)
Mainly corticolous (81%), may grow also on rocks (19%) (Clerc 1987b). Reported in Europe: Belgium, Bulgaria, Czech Republic (probably extinct), France (probably extinct), Germany, Great Britain, Italy, Luxembourg (probably extinct), Netherlands (probably extinct), Norway, Poland, Portugal, Romania, Switzerland, Spain.