Usnea glabrata (Ach.) Vain.

Nomenclatural data
Ann. Acad. Sci. Fenn., Ser. A4, 6(7): 7 (1915).—Usnea plicata (L.) F.H. Wigg. var. glabrata Ach., Lichenogr. Univ.: 624 (1810).—Usnea sorediifera (Arnold) Lynge, Skr. Vidensk.-Selsk. Christiana, Math.-Naturvidensk. Kl. 7: 229 (1921).
Morphology
For a detailed description, see Myllys (1994), Halonen et al. (1998, 1999) and Clerc (2007). Thallus shrubby, small (not exceeding 5 cm, often less); branches somewhat inflated, foveolate and constricted at ramification points; base of the same colour as the rest of the thallus; fibrils numerous; isidiomorphs absent; papillae usually absent; conspicuous soralia mostly near the apices of branches and fibrils, large and may become confluent. Cortex thin, shiny; medulla thick, very loose; central axis thin.
Medullary chemistry
(1) chemotype with protocetraric and fumarprotocetraric acids as main compounds (K± brownish, Pd+ red) and several substances as accessories is known in Europe and North America; (2) chemotype with salazinic and norstictic acids as main substances (K+ red, Pd+ yellow to orange) and with different accessory compounds has been reported from Fennoscandia (Halonen et al. 1999); (3) acid deficient chemotype without medullary substances (K–, Pd–) has also been mentioned (Clerc 1987b, Myllys 1994, Brodo et al. 2001).
In Estonia chemotype (1) is common (n=7) (Tõrra & Randlane 2007).
Remarks
Easily recognized by morphological characters (small shrubby thallus, constriction of secondary branches at their base, presence of rather large soralia, and absence of both papillae and isidiomorphs). Medullary chemistry is of great help in case of chemotype (1) as fumarprotocetraric and protocetraric acids do not occur as main compounds in other shrubby species.
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Ecology and distribution
Europe (map legend)
Corticolous. Reported in Europe: Austria, Belgium, Bulgaria, Czech Republic (probably extinct), Denmark, Estonia, Finland, Germany, Great Britain, Hungary, Italy, Lithuania, Norway, Poland, Portugal, Romania, Russia, Slovakia (probably extinct), Slovenia, Spain, Sweden, Switzerland, Ukraine.

Estonia
78% of examined specimens grow on Picea, and 11% both on Pinus and on Betula; other substrates are not known for this Usnea in Estonia (Tõrra & Randlane 2007) while Alnus is the prevailing phorophyte in Finland and Russian part of East Fennoscandia (Myllys 1994). Rather frequent (13 specimens), reported mainly in paludified forests in southern and south-eastern regions of Estonia; still, latest collection dates back to 1959. Not recorded in Latvia, and in Lithuania only one verified locality is known (Motiejūnaitė 2002).