Usnea wasmuthii Räsänen

Nomenclatural data
Ann. Acad. Sci. Fenn., Ser. A4, 34(4): 19 (1931).
For a detailed description, see Clerc (1992, 2007) and Halonen et al. (1999). Thallus shrubby or rarely subpendent, rather richly branched, branches gradually tapering; branching mainly isotomic-dichotomous; base distinctly blackened, often with both transverse and longitudinal cracks; fibrils present, but usually few near apices; isidiomorphs short, few, present on young soralia (and abraded on mature soralia); papillae present; soralia small to enlarged, oblong-cylindrical, slightly excavate. Cortex thick; medulla thin, dense.
Medullary chemistry
Altogether five chemotypes have been registered (Clerc 1992; Halonen et al. 1999; Fos & Clerc 2000; Ohmura 2001): (1) chemotype with barbatic acid (K–, Pd–) as the main substance; (2) chemotype with salazinic acid (K+ red, Pd+ yellow to orange) as the main substance; (3) chemotype with both barbatic and salazinic acids (K+ red, Pd+ yellow to orange) as main substances; (4) chemotype with thamnolic acid (K+ yellow, Pd+ orange); (5) chemotype without medullary compounds (K–, Pd–). Different accessory compounds (protocetraric, 4-O-demethylbarbatic, psoromic acids) may occur in two first chemotypes, and squamatic acid additionally in the chemotype (4). The latter (recorded in Japan and Spain) has also been considered a possible hybrid since thamnolic and squamatic acids are typical compounds for U. subfloridana.
In Estonia chemotype (1) is common (n=15) and chemotype (3) is rare (n=3) (Tõrra & Randlane 2007).
Veli Räsänen named this taxon after a German person Paul Wasmuth (1874–1934), an estate owner in Russia, who lived and worked as a journalist in Estonia, Tallinn. He was mainly interested in birds and plants but also used to collect lichens; unusual specimens were sent to Räsänen for the identification. The type specimen (Estonia, Harjumaa, Tallinn, Kakumäe; preserved in H) was collected by him in 1908.
Distinction from closely related taxa see under U. fulvoreagens.
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Ecology and distribution
Europe (map legend)
Corticolous. Reported in Europe: Austria, Belgium (probably extinct), Bulgaria, Estonia, Finland, Germany, Great Britain, Hungary, Ireland, Italy, Lithuania, Luxembourg, Norway, Poland, Romania, Slovakia, Spain, Sweden, Switzerland.

Grows mainly on Picea (29% of examined specimens) and on Betula (29%), while on Pinus it has been observed only occasionally (6%). 33% of examined specimens grow on other conifers and 11% on other deciduous trees (Tõrra & Randlane 2007). Rather frequent in Estonia (20 specimens), found on the northern coast, south-eastern region of the mainland and the western islands.