Usnea hirta, Usnea hirta
Thallus 1-4 cm tall, ± tufted, erect, shrubby or rarely subpendant, notably flaccid when wet, main branches to 1 mm diam, angular or irregular (not round) in cross-section, ± slightly swollen. Surface often with inconspicuous, net-like ridges surrounding ill-defined depressions, richly branched, papillae absent, fibrils few or absent, grey-green, yellow-green or blackish grey, not blackened at the base. Isidia abundant, scattered or densely clustered, short and spinule-like, sometimes arising from the ridges. Cortex thin, medulla rather lax, axis relatively thin.
Anamorph: not known.
Teleomorph: ascomata (apothecia) rarely seen.
Chemistry: thallus C–, K–, KC–, Pd– (usnic and ± fatty acids [murolic acid complex]); reported K+, Pd+ specimens are probably due to contamination.
Locally frequent. Assessed as of Least Concern by Woods & Coppins (2012).
Distinguished by the ± angular main branches, the flaccid and limp habit when wet, absence of papillae or tubercles, abundant long, spinule-like isidia and the absence of a blackened base. A very variable species, consisting of few, ± pendulous, contorted strands to small, erect, densely tufted and compact thalli.
Usnea subfloridana and U. wasmuthii are not flaccid when wet, and have a different chemistry. In addition, isidia and isidiomorphs are associated with soralia and usually in clusters, and the branches have papillae and are terete (round in section) and have a blackened basal part.
Predominantly E & N British Isles, rare in W & S England. It is interesting to note that in Holland this species is recolonising in urban areas (roadside trees, etc) where it is tolerant of some degree of eutrophication; its recent occurrence in Kew Gardens, London, may signify a similar tolerance.
Most frequent on conifers, more rarely on wayside and woodland acid-barked deciduous trees, especially Betula and Quercus, decorticated wood and Calluna stems.