Usnea (All Fungi)
Thallus shrubby, erect to elongate- pendent or decumbent, in most species attached by a compact holdfast that may be concolorous with the thallus or brown-black. Branching patterns varied. Branches rounded to angled, even and smooth or pitted, with a network of ridges, shiny or matt, occasionally with annulations or jointed, then divided into segments which may be swollen and ± constricted at their point of attachment, with or without fibrils, tubercles, papillae and pseudocyphellae. Soredia present in most species, isidia and/or isidiomorphs (isidia arising from soralia) present in many. Outer cortex present. Medulla lax or compact. Central axis a cartilaginous strand of solid, tough, compacted, longitudinally arranged hyphae, white, rarely pinkish or yellow. Photobiont trebouxioid.
Anamorph: conidiomata pycnidia, mainly terminal or subapical. Conidia simple, colourless, bacilliform, bifusiform, thickened at one or both ends, straight or curved.
Teleomorph: ascomata apothecia, lateral or terminal; disc rounded, flat or concave. Thalline exciple persistent, often with short, ray-like projections. Asci 8-spored, elongate-clavate, Lecanora-type. Ascospores simple, ellipsoid, colourless.
Chemistry: usnic acid in the cortex of all species, the medulla with range of depsides, depsidones or fatty acids.
The ‘beard lichens’ somewhat resemble species of Evernia and Ramalina, which also grow as grey-green or yellow-green tufts on trees, but these in most cases have a flattened, less branched thallus and lack an elastic, cartilaginous central axis.
On acid- and basic-barked tree branches and trunks, more rarely on cut wood (fence posts etc.) and rocks.