Usnea cornuta  

Thallus 2-6(-10) cm, ± erect, tufted, rarely subpendent. Main branches to 1.5 mm diam., inflated, with few to numerous, short, lateral branches, clearly constricted and often annulated at the point of attachment to the main stems, mostly curved, often widely divergent to 90° in terminal branches, branching anisotomic dichotomous, predominantly isotomic towards apices. Cortex surface dull grey-green becoming ± dark brown in the herbarium, often smooth and ± shiny-glassy in lower parts of main branches, more rarely corrugate-areolate, sparsely to densely papillate, papillae absent on the upper branches. Base usually concolorous or paler, rarely blackened. Medulla very lax. Scattered or clustered isidia-like structures (isidiomorphs) present together with ± roughened, whitish grey, erose, ± erumpent soralia. Soralia minute, 0.06-0.2 mm diam., numerous, often becoming confluent and spreading. Soredia coarsely granular, often mixed with a few to many secondarily corticate isidiomorphs.

Anamorph: not known.

Teleomorph: not known.

Chemistry: two chemotypes occur: (a) K+ yellow→red, Pd+ yellow to orange-red (salazinic and ± protocetraric and ± constictic acids); (b) K+ yellow→blood-red, Pd+ yellow-orange (stictic [major], norstictic, menegazziaic, constictic and ± salazinic acids). The two chemotypes are equally frequent.