[Translated and modified from Motyka (1936-1938)] Thallus pendant, ~ 15 cm long, tight and fairly compressed, sparingly branched, with several secondary branches, regularly although not often noticeably branched, tight and firm, dark green, in herbarium olivaceous, branches, thinner, paler; base slightly or rarely not attenuated, usually slightly thickened above, almost immediately branched sympodially, branches narrow. Primary branches are branched, the branches arcuately dependent but distinctly narrow. Secondary branches thickened above the base, usually ~1.2 mm thick, regularly fusiform tapering, rarely transversely broken, smooth, regularly and delicately papillate along its entire length; papillae minute, acute. Lateral branches not frequent, regularly arranged, 0.5-1.5 cm long, perpendicular, often gracefully curved above, gradually tapering, slightly papillate. The tips are short, thin, usually curved and dichotomously branched. Thallus stratified: cortex 60 μm thick; medulla of loose hyphae, 200 μm thick; axis 150 μm diam. Ascomata lecanorine apothecia, numerous, subapical on lateral branches, short, small, cup-like, often several per branch. Thalline rim with marginal fibrils of various length; disk concave, often white-pruinose. Asci 8-spored; ascospores simple, hyaline, 7 x 10 um.
Chemistry. Medulla K-; otherwise not reported.
Substrate and habitat. Corticolous on branches.
Distribution. Europe, North America, primarily the Pacific Northwest; in North Carolina represented by a single specimen in the Blue Ridge ecoregion.
Note. Usnea quasirigidula was established as a replacement name for the taxonomically confusing U. rigida Motyka (Lendemer & Tavares 2003).
Literature
Lendemer, J.C. & I.I. Tavares (2003) Nomenclature and typification in the genus Usnea (lichenized Ascomycetes)—I. Usnea rigida. Proceedings of the Academy of Natural Sciences of Philadelphia153(1): 177-180.
Motyka, J. (1936-1938) Lichenum generis Usnea studium monographicum, pars systematica 1-2: 1-651 (original description as Usnea rigida).