Usnea galapagona Truong & P. Clerc
Mycobank MB 518904
Thallus fruticose, up to 8 cm long, erect and strongly shrubby, often with several attachment points. Base concolorous with thallus, usually with a reddish tinge. Branching distinctly anisotomic-dichotomous. Branches irregular to tapering, not constricted at their attachment point. Section of branches terete to slightly flattened or ridged. Terminal branches with few divisions and thickened at the tips. Fibrils few or absent. Papillae hemispherical, often numerous. Soralia minute, often aggregating in small packs or fusing thus looking like a large single soralia, developing on top of papillae or directly on the cortex ad initio, remaining plane with a distinct cortical margin, rarely becoming slightly stipitate or efflorescent, but never excavating. Isidiomorphs present, very small. Apothecia not seen. Cortex thick (15.5–19.5% of branch width, n = 10), very hard and vitreous in longitudinal section of branch. Medulla compact, usually very thin and almost indistinct (3–4.5%), rarely thicker (up to 10%) close to the base. Axis very thick (54.5–62%). Medulla K–, C–, P–. Secondary metabolites detected by thin layer chromatography (n = 9): usnic acid and an unknown compound reacting UV+ green after charring (RF classes: solvent A = 6; B = 3; C = 5).
Usnea is a large genus of c. 350 mainly corticolous species, principally corticolous (Swinscow & Krog, 1979; Clerc, 1987, 2006, 2008; Halonen et al., 1998; Herrera-Campos et al., 1998; Ohmura, 2001; Stevens, 2004). The genus is characterized by the fruticose thallus, branches holding a central axis and the presence of usnic acid in the cortex (Clerc, 1998). This new species, so far endemic to the Galápagos, is characterized by anisotomic-dichotomous branching, terminal branches with few divisions, the absence of fibrils and the minute soralia developing from low papillae or on the cortex of branches, often aggregating in packs or fusing. Anatomy in longitudinal section of branch is very characteristic, with a thick, very hard and vitreous cortex, a thick axis and a very thin, almost indistinct medulla. TLC analysis revealed the presence of a new unknown substance in the medulla, reacting UV+ green after charring. The cortex of U. subscabrosa Motyka (Herrera-Campos et al., 1998) is similar to U. galapagona, but the former species is pendulous, with a very different morphology, chemistry and ecology.
The epithet refers to the location where this species was discovered.
Endemic to the Galápagos Islands, so far known from Isabela, Sán Cristóbal and Santa Cruz Islands. This species usually grows on exposed habitats, for instance along ridges or on the slopes of the volcan’s crater. It was found in the transition vegetation zone, seldom in the arid and humid zones. Substrate: on rocks, on cactus and more rarely on bark (for exemple trunks of Bursera graveolens).
Type:—ECUADOR: Galápagos Islands: Isla Sán Cristóbal, Cerro Mundo, at the top of the rock cliffs on the S side close to the summit; 00°53’S, 89°34’W, 282 m; transition zone with Bursera graveolens, Croton scouleri and Jasminocereus thouarsii, on Jasminocereus thouarsii on the ridge; Aug 2008, Clerc & Truong 08-405 (holotype CDS; isotypes G; CMA: 16/3/61.5; chemistry: usnic acid, unknown medullary metabolite reacting UV+ green after charring).
Additional specimens examined (paratypes):— ECUADOR: Galápagos Islands: Isabela, Volcán Alcedo, Aptroot 64769A (CDS). Isabela, Volcán Darwin, SW slope, Bungartz 7862B (CDS). Sán Cristóbal, sector of the gotera de agua, Clerc & Truong 08-330 (CDS, G). Santa Cruz, N side of the island, Aptroot 64568 (CDS
Thallus erectus; basi leviter rubescens; ramuli irregulares; soralia punctiformia, interdum agregata vel conjuncta; cortex nitidus et valde crassus (proportione 16–18%); medulla valde tenuis (3–4.5%) et K– (substantiam incognitam et UV+ viridis continente).