Usnea erinacea Vain. Dansk bot. Ark.4(11): 3 (1926).
Short Description. For a detailed description see Clerc (2004, 2007) and Herrera-Campos (2016); this typically fertile species is characterized by a red-orange cortex. It has regularly terete branches gradually tapering, not constricted at their attachment point. Apothecia, if present, are sub-terminal to terminal. When apothecia are missing, specimens can usually still be identified, because branch apices then typically bear numerous pycnidia in spherical protuberances. The species has a thick and shiny cortex (9 –14 %), a compact medulla (11.5 –21 %) and an medium to large axis (36 –53.5 %) , with an A/M-ratio > 1.5. Molecular data suggests that U. erinacea (non-sorediate) and U. rubicunda (sorediate) are part of the same large species complex, in which lineages do not necessarily segregate based on the presence of soralia (Truong et al. 2013a). More studies of representative material from various regions in the world are needed to better understand the phylogeny in the group. Although specimens with both apothecia and soralia were not observed among Galapagos specimens the phylogeny of U. erinacea/rubicunda remains unresolved; for convenience the two taxa continue to be treated here as two separate species.
Chemistry. Medulla with salazinic and norstictic acid [P+ yellow, K+ yellow turning deep red (±crystals), C–, KC–]. Only chemotype 2 (salazinic and norstictic acid) is known from the Galapagos. On the continent this chemotype is rare, where chemotype 1 (stictic acid), 3 (norstictic acid only) and 4 (triterpenoids only) occur more frequently (Truong et al. 2011).
Ecology and distribution. An almost cosmopolitan taxon (North and South America, western Europe, southern and eastern Africa). Throughout the Neotropics U. erinacea is generally less common than its sorediate counterpart U. rubicunda. This is also the case for the Galapagos, where fertile specimens are rare, but their sorediate counterpart is among the most common and abundant Usnea species found. In Galapagos U. erinacea occurs in the dry and transition zone, typically in open vegetation (Bursera woodland, Croton scrub).
Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Thallus: erect-shrubby to subpendant, 2-15 cm long branching: anisotomic-dichotomous, divergent basal part: concolorous with branches branches: tapered, lateral branches not narrowed at attachment points segments: terete, cylindrical papillae: nearly absent to numerous (young fibrils?) tubercles: absent fibercles: few to numerous fibrils: numerous, short (< 3mm) and thick, giving a spinulous aspect to the branches isidiomorphs: absent pseudocyphellae: absent cortex: thick (9-12%), shiny with a red pigment sometimes spotty and sparse at the surface medulla: compact, thin to moderately thick, sometimes ±slightly orange pigmented axis: thick, fistulose in the thickest branches Apothecia: usually present, sometimes nearly absent, subterminal to terminal Spot tests: medulla K+ yellow turning red, C-, KC-, P + orangish yellow Secondary metabolites: medulla with norstictic (major) and salazinic (major) acids and ±protocetraric acid (minor). Substrate and ecology: on bark of Quercus at 2300 m in mixed pine-oak forest World distribution: East Africa, southern North America and South America (?) Sonoran distribution: Sierra Madre Occidental of Sinaloa. Notes: Usnea erinacea is easily distinguished from all other species of the area by its numerous apothecia, the absence of soralia, its red pigmented cortex, and its chemistry.