Usnea substerilis Motyka

Nomenclatural data
Wydaw. Muz. Slask. Katowic. 3(2): 24 (1930).—Usnea sorediifera Motyka, Wydaw. Muz. Slask. Katowic. 3(2): 24 (1930), nom. illeg., non Usnea sorediifera (Arnold) Lynge (1921).—Usnea stuppea (Räsänen) Motyka
Morphology
For a detailed description, see Halonen et al. (1998, 1999) and Clerc (2007). Thallus shrubby, usually short, richly branched; branching mainly anisotomic-dichotomous; base pale to blackened; branches of uneven thickness, may be irregularly deformed, swollen and foveolate, with annular cracks which may have white medullary rings; fibrils present, sometimes abundant also terminally; isidiomorphs short, present at least on young soralia (and abraded on mature soralia); papillae numerous; soralia irregular, slightly tuberculate to slightly excavate, with granulose soredia. Cortex thin; medulla variable in thickness and density.
Medullary chemistry
(1) the main chemotype contains salazinic acid (K+ red, Pd+ yellow to orange) with different accessory substances (protocetraric, barbatic, 4-O-demethylbarbatic acids); (2) chemotype without medullary compounds (K–, Pd–) is also known (Halonen et al. 1998).
In Estonia both chemotypes are recorded (n=6 and n=4, respectively), chemotype (1) is prevailing (Tõrra & Randlane 2007).
Remarks
Distinction from closely related taxa see under U. diplotypus.
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Ecology and distribution
Europe (map legend)
Corticolous both on coniferous and on deciduous trees. Reported in Europe: Austria, Bulgaria, Estonia, Finland, Germany, Italy, Latvia, Lithuania, Norway, Poland, Romania, Russia, Slovakia, Spain, Sweden, Switzerland, Ukraine.

Estonia
Grows mainly on deciduous trees (on Betula 17% of examined specimens, on other deciduous trees 33%); conifers are inhabited less often (Picea 17%, Pinus 8%, other tree species 15%) than by most Usnea species. Rather rare in Estonia (10 specimens), found scattered in all regions of Estonia (Tõrra & Randlane 2007).