Usnea diplotypus Vain.

Nomenclatural data
Medd. Soc. Fauna Fl. Fenn. 48: 172 (1925)
Morphology
For a detailed description, see Halonen et al. (1998, 1999). Thallus shrubby, often subpendent; base pale or blackened; branching mainly anisotomic-dichotomous; branches of uneven thickness, may be irregularly swollen and have depressions, branch tips often twisted; fibrils and papillae present but their number is variable; isidiomorphs frequently numerous and relatively long; soralia punctiform and usually not expanding, soredia farinose. Cortex thin; medulla variable both in density and thickness.
Medullary chemistry
Salazinic acid (K+ yellow, orange or red, Pd+ yellow to orange) is present as a main substance, and protocetraric, barbatic, 4-O-demethylbarbatic and alectorialic acids occur as accessories in Europe and North America (Clerc 1987b; Halonen et al. 1998).
This chemotype is common also in Estonia (n=18) (Tõrra & Randlane 2007).
Remarks
Close to U. lapponica and U. substerilis: all these taxa have more or less shrubby thallus, anisotomic-dichotomous branching, and branches of uneven thickness, with occasional foveolae and depressions. U. diplotypus often has subpendent thallus, twisted branch tips and comparatively long isidiomorphs while on U. substerilis short isidiomorphs are present only on young soralia, and on U. lapponica they are totally absent. All three species have similar chemotypes (with salazinic acid as a main substance) and therefore identification of medullary compounds is no help for distinguishing these taxa.
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Ecology and distribution
Europe (map legend)
Corticolous. Reported in Europe: Austria, Bulgaria, Czech Republic, Estonia, Finland, Germany, Hungary, Italy, Lithuania, Norway, Poland, Russia, Slovenia, Spain, Sweden, Switzerland.

Estonia
Grows mainly on Picea (39% of examined specimens) and Betula (20%), more rarely on other deciduous trees (e.g. Acer) (7%), Pinus (7%) or lignum (7%) in coniferous or mixed forests (Tõrra & Randlane 2007). Rather frequent in Estonia (18 specimens), found mainly along the northern coast; not known in Latvia.