Usnea chaetophora Stirt.

Nomenclatural data
Scott. Naturalist Nov. Ser. 1: 76 (1883).—Usnea leiopoga Motyka, Lich. Gen. Usnea Stud. Monogr. Pars. Syst. 1: 187 (1936).
Morphology
For a detailed description, see Halonen et al. (1998). Thallus pendulous, with numerous and smooth branches; most branches are divided by annular cracks into regular segments up to almost terminal parts; fibrils, isidiomorphs and papillae absent or scarce; soralia few, punctiform. Cortex rather thick; medulla thin and dense.
Medullary chemistry
Two chemotypes have been recorded by Halonen et al. (1998) from Canada, British Columbia: (1) chemotype with salazinic acid as a main substance (K+ yellow, orange or red, Pd+ yellow to orange) is more usual; (2) chemotype without medullary substances (K–, Pd–) occurs occasionally.
In Estonia both chemotypes are known (n=1 either) (Tõrra & Randlane 2007).
Remarks
 Pendulous thallus, absence (or scarce presence) of fibrils and isidiomorphs, and annulation of branches throughout the thallus (not only at the base) are the diagnostic characters. Sometimes may resemble U. barbata and then consistence of medulla should be checked again (dense medulla in U. chaetophora, and loose in U. barbata).
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Ecology and distribution
Europe (map legend)
Corticolous. Bulgaria, Estonia, Germany, Great Britain, Norway, Poland, Slovakia, Spain, Sweden, Ukraine

Estonia
Grows on branches of Picea in fresh boreal forests. Very rare in Estonia, recorded twice in southern and south-eastern regions (Tõrra & Randlane 2007); not known in Latvia or Lithuania.