The species belongs to the taxonomically difficult U. cornuta agg. (Gerlach et al. 2020), previously to the broader U. fragilescens agg. (Clerc 1987). They all represent smaller Usnea species with fruticose to semi-pendent thalli, often gradually widening (fusiform) or even inflated side branches, constricted at the branching point.
In Europe, the species of the group have a strongly oceanic distribution (Clerc 1987, Gerlach et al. 2020). They are mostly epiphytes, although the type of U. cornuta s. str. is saxicolous on sandstones in the Harz Mts in central Germany. Its presence in the Czech Republic remains questionable; the herbarium material has not been found (Černohorský et al. 1956), but its historical occurrence is possible.
Most of the historical records published under the name U. cornuta are regarded synonymous to U. diplotypus (= U. dasopoga) in the catalogue of the Czech lichens (Vězda & Liška 1999). That is because all the saxicolous specimens from north Bohemian sandstones, originally named U. cornuta and later described as U. saxicola (Anders 1928) were synonymized with U. diplotypus by Keissler (1960) in his monography of central-European Usnea species.
Within the U. cornuta agg., only the recently described U. arianae is currently known in central Europe. The type material is from Switzerland. The species is distinguished by a common presence of lobaric acid and unknown fatty acids which are not known in U. cornuta s. str. (Gerlach et al. 2020).
Literature: Anders J. (1928): Die Strauch- und Laubflechten Mitteleuropas. Anleitung zum Bestimmen der in Mitteleuropa vorkommenden Strauch- und Laubflechten. – G. Fischer, Jena. Černohorský Z., Nádvorník J. & Servít M. (1956): Klíč k určování lišejníků ČSR. I. díl. – Nakladatelství ČSAV, Praha. Clerc P. (1987): Systematics of the Usnea fragilescens aggregate and its distribution in Scandinavia. – Nordic Journal of Botany 7: 479–495. Gerlach A., da Silveira R. M. B., Rojas C. & Clerc P. (2020): Naming and describing the diversity in the Usnea cornuta aggregate (lichenized Ascomycota, Parmeliaceae) focusing on Brazilian specimens. – Plant and Fungal Systematics 65: 272–302. Keissler K. (1960): Usneaceae. – In: Rabenhorst's Krypt.-Fl., Teil 4: 1–755, Leipzig.
taxonomic classification:Ascomycota → Lecanoromycetes → Lecanorales → Parmeliaceae → Usnea
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