Usnea glabrata, the lustrous beard lichen, is a species of beard lichen in the family Parmeliaceae. This small, shrubby species typically grows 5–10 centimetres tall. Distinguished by its somewhat shiny surface, slender branches that taper at both ends, and the presence of powdery reproductive structures near the branch tips, this lichen primarily grows on tree bark in moderately open, humid forests throughout boreal and temperate regions of the Northern Hemisphere. U. glabrata is considered vulnerable in parts of its range due to its small size making it easy to overlook and its relatively sparse collection in recent decades.
Taxonomy
It was first described as a variety of Usnea plicata by Erik Acharius. Finnish lichenologist Edvard August Vainio transferred it to the genus Usnea in 1915. Key distinguishing characters of the species are the small shrubby thallus, constriction of secondary branches at their base, presence of large soralia, and the absence of both papillae and isidia.
In North America, it is commonly known as the "lustrous beard lichen".
Description
Usnea glabrata forms a small, erect thallus (body) that typically reaches up to 5–10 cm in height. The thallus is sparsely to densely branched, with the branching pattern primarily anisotomic-dichotomous (where dividing branches are unequal in thickness). The branches are generally slender, measuring up to 1.5–1.8 mm in diameter, and are characteristically inflated with a somewhat swollen appearance. They often display foveoles (small pit-like depressions on the surface) and are typically constricted or fusiform (tapering at both ends) at their bases. Branch tips commonly curve backwards.
The surface of U. glabrata has a somewhat shiny appearance, which distinguishes it from many other Usnea species that have a matt surface. This feature is typical for species in the U. fragilescens group. The cortex (outer protective layer) is thin, comprising only 4–5–7% of the branch...
