Usnea longissima Ach.

Nomenclatural data
Lichenogr. Univ.: 626 (1810).
 For a detailed description, see Halonen et al. (1998). Thallus pendulous, long to extremely long (up to 3 m); base pale to blackened; the main stem is only some mm long, covered with persistent cortex; numerous primary branches are almost undivided, with numerous perpendicular fibrils; papillae absent; isidiomorphs and soralia occasionally occur on side branches or fibrils. Cortex disintegrated on the primary branches exposing the thin compact medulla; central axis very thick, originally white but becoming pink to almost red or brown in decorticated branches. I+ blue reaction on the central axis is of help in identification of juvenile specimens.
Medullary chemistry
Several chemotypes have been reported; diffractaic, evernic and barbatic acids (all react K–, Pd–) seem to be the most common substances in U. longissima in Europe and North America (Halonen et al. 1998) while salazinic and fumarprotocetraric acids and atranorin are additionally known in Japan (Asahina 1967).
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Ecology and distribution
Europe (map legend)
The species is distributed in the northern hemisphere, having circumboreal distribution pattern and occurring in humid forests, often near lakes or streams (Nimis 1993, Brodo et al. 2001). Corticolous, e.g. in eastern Fennoscandia it has been recorded on Picea and Betula (Halonen 1997). Reported in Europe: Austria, Bulgaria, Czech Republic (probably extinct), Finland, Germany, Italy, Latvia, Norway, Poland, Romania, Russia, Slovakia (probably extinct), Slovenia, Spain, Sweden, Switzerland, Ukraine.

Listed in Estonia according to a record from the beginning of the 20th century in the vicinity of Tallinn, Aegviidu (Charlottenhof), in the northern part of the country (Mereschkowski 1913); no herbarium specimens preserved. In Latvia reported from the northern region, Mazsalaca (Piterāns 1982, 2001); in Lithuania not known.