Usnea cornuta (All Fungi)
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.
Considered to be of Least Concern (Woods & Coppins 2012). The species is widely distributed and locally frequent in lowland areas, and returning to many previously air-polluted habitats. Probably the commonest species on trees in SW England and Wales.
A very variable, widespread and common species occurring in two equally frequent and widespread chemical races. It is characterized by the shrubby habit, often divergent and claw-like appearance of the main and terminal branches, dark green colour (yellow-green in very exposed sites), ± inflated, widely divergent main branches which are markedly constricted and often annulated at their point of attachment. The widely divergent branching pattern gives a distinctive 'electrocuted' look. Small papillae are present, also minute soralia which coalesce to form extensive soralia-like areas. These produce granular soredia and few to many, fragile, secondarily corticate isidia (isidiomorphs) and spinules. The main branches often yield with a ‘crack’ to pressure from a fingernail.
U. flammea, which often occurs in similar habitats, has pale annulations on its main stems, lacks inflated attenuated branches and generally has a smoother surface. U. fragilescens differs in the size and density of soralia and chemistry.
In GB&I, widely distributed in the W and SW British Isles, rarer in eastern regions.
On mossy, usually broadleaved woodland or wayside trees, more rarely siliceous rocks.