Usnea subfloridana Stirt.

Nomenclatural data
Scott. Naturalist 6: 294 (1882).—Usnea comosa (Ach.) Vain., Meddel. Soc. Fauna Fl. Fenn. 48: 173(1925), nom. illeg., non Usnea comosa Pers.—Usnea similis (Motyka) Räsänen, Ann. Acad. Sci. Fenn., Ser. A4, 34(4): 19 (1931).
Morphology
For a detailed description, see Halonen et al. (1998, 1999). Thallus shrubby to subpendent, richly branched; branching mainly isotomic-dichotomous; base clearly differentiated and blackened, often with transverse annular cracks; fibrils present, abundant near the base and sparse terminally; isidiomorphs and papillae usually numerous; soralia vary from punctiform to enlarged and typically bear short isidiomorphs. Cortex rather thick; medulla thin and dense.
Medullary chemistry
Three chemotypes are reported: (1) with squamatic acid (K–, Pd–, UV+ whitish blue) as a main substance; (2) with thamnolic acid (K+ yellow, Pd+ orange) as a main substance; (3) with both squamatic and thamnolic acids (Halonen et al. 1998, 1999). Alectorialic acid may occur as an accessory.
In Estonia two first chemotypes are known (n=37 and n=31, respectively). (Tõrra & Randlane 2007).
Remarks
Usually easily recognized by black base and presence of numerous isidiomorphs. Sometimes may be mixed up with U. diplotypus or with U. wasmuthii, then the identification of medullary substances would help – squamatic or thamnolic acids which are the main compounds in U. subfloridana are usually absent in U. diplotypus and U. wasmuthii [except the chemotype (4) of the latter].
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Ecology and distribution
Europe (map legend)
Corticolous, occasionally also lignicolous or on rocks. Reported in Europe: Austria, Belgium, Bulgaria, Czech Republic, Denmark, Estonia, Faeroe Islands, Finland, France, Germany, Great Britain, Hungary, Ireland, Island, Italy, Latvia, Lithuania, Luxembourg, Norway, Poland, Portugal, Romania, Russia, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Ukraine.

Estonia
Grows mainly on conifers (on Picea 35% of examined specimens, on Pinus 18%, on other 14%) and on Betula (22%), rarely on other deciduous trees (7%) and lignum (4%); has been reported also on rocks (0,3%) (Tõrra & Randlane 2007). Very frequent in Estonia, found in all regions of Estonia.