Usnea florida (L.) F.H. Wigg.

Nomenclatural data
Prim. Fl. Holsat. 2: 7 (1780).—Lichen floridus L., Spec. Plant. 2: 1156 (1753).—Usnea tominii Räsänen in Tomin, Trudy Tyflissk. Bot. Inst. 1: 371 (1933).
For a detailed description, see Clerc (1984) and Purvis et al. (1992). Thallus shrubby; base blackened; fibrils numerous, becoming curved at the tips; isidiomorphs absent, papillae abundant, low, mostly on main branches; soralia absent; apothecia frequent, arising at apices of primary and secondary branches, with long (up to 5 mm) marginal projections. Ascospores 8–11 μm. Cortex rather thick; medulla thin, dense.
Medullary chemistry
Two chemotypes are known in Europe: (1) with thamnolic acid as a major substance (K+ yellow, Pd+ orange) and alectorialic acid as an accessory substance (in apothecia, K+ yellow, Pd+ yellow, KC+ red on disc); (2) with squamatic acid (K–, Pd–) (Clerc 1984; Articus et al. 2002). Chemotype (1) is prevailing (Clerc 1984). Clerc (2007) reported chemotype (3) with salazinic acid as a major substance and norstictic acid as an accessory from North America, Sonoran region but is unsure whether this chemotype can be accepted as U. florida s. str.
The taxon is typically richly fertile and always lacking any vegatative propagules (soralia or isidiomorphs). Specimens with both soralia/isidiomorphs AND apothecia (usually with only a few apothecia) are assigned to U. subfloridana (James 2003).
Differs from another fertile European taxon, U. intermedia, by clearly shrubby thallus and by longer ascospores (7–8.5 μm long in U. intermedia). Positive Pd and KC colour tests on the apothecial disc are useful for the identification of U. florida specimens belongig to the more widely distributed chemotype (1), with thamnolic and alectorialic acids.
U. florida is considered to be the primary, fertile counterpart in a species pair where U. subfloridana is the sterile, secondary counterpart (Clerc 1984). Still, phylogenetic analyses have demonstrated that the specimens of these two taxa do not form two monophyletic clades according to the way of reproduction but fall into one intermixed group (Articus et al. 2002).
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Ecology and distribution
Europe (map legend)
Corticolous, prefers to grow on old deciduous trees in areas with high atmospheric humidity, but has been reported also from conifers (e.g. Abies and Picea) (Clerc 1984). Serious decline is recorded or suspected due to rising levels of eutrophication (James 2003). Recorded in Europe: Albania, Austria, Belgium, Bosnia, Bulgaria, Czech Republic, Denmark (probably extinct), France, Germany, Great Britain, Hungary, Italy, Latvia, Lithuania, Luxembourg, Netherlands, Norway, Poland, Portugal, Romania, Russia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Ukraine.

Not known in Estonia (Tõrra & Randlane 2007) but recorded in Latvia (Piterāns 1982, 2001) and Lithuania (Motiejūnaitė 1999). Occurrence in south-western Estonia can be presumed.