For a detailed description see Truong et al. (2011).
Short Description.Usnea subcornuta is characterized by a reddish orange subcortical pigmentation, visible in section of its inflated branches, which are distinctly constricted at their attachment point. The species has a relatively thick and very loose medulla (A/M-ratio > 1). It is further characterized by slender, scattered fibrils and minute soralia with few isidiomorphs.
Usnea cornuta (Clerc 2007; Herrera-Campos et al. 2001) exhibits a very similar morphology and chemistry, but it lacks the orange subcortical pigmentation present in the medulla of U. subcornuta [the main reason why Clerc (1987) treated both as distinct species]. In Galapagos, U. subdasaea shares with U. subcornuta the orange subcortical pigmentation, but differs in its chemistry (galbinic acid) and the irregular branches, which are, at least in part, densely covered with numerous spinulose fibrils and isidiofibrils.
Chemistry. Medulla with stictic, and ±norstictic acid (traces), ±tri-terpenoids (traces) [P+ deep orange, K+ yellow slowly turning red, C–, KC–].
Ecology and distribution. Originally known from southwestern Europe, North Africa and western Asia (Clerc 1987, Fos & Clerc 2000). Truong et al. (2011) added only few collections from continental South America. Although its orange subcortical pigmentation is very conspicuous, this species has a very small size and may thus easily be overlooked. Nevertheless U. subcornuta has never been found abundantly and the few known records suggest that, at least in the Neotropics, this species is generally rare. The three specimens now reported from the Galapagos also suggest that the species is not common. Two collections are from the same site, in the transition zone of Santa Cruz (above Mina Granillo Rojo; a site sadly being destroyed by the quarry), while another specimen was collected on Pteridium in the humid zone of the same island.
Despite morphological similarity (distinguished by the presence or absence of medullary pigmentation) U. subcornuta and U. cornuta generally display distinctly different distribution patterns: Usnea cornuta is cosmopolitan, very common throughout the Neotropics, found along a broad altitudinal range; Usnea subcornuta, on the other hand, is rare, globally scattered, and in the Neotropics only known at low altitudes. Based on the few specimens of U. subcornuta so far discovered in the archipelago, it is nevertheless difficult to assess, if, in the archipelago, these two species differ significantly in their ecology.