Mycobank MB 517816
Thallus approx. 5–7 cm, arising from a proliferating, unpigmented or brownish holdfast with main branches tapered towards the holdfast; erect, shrubby, subdichotomous to richly branched with terete branches; thallus surface yellow-green, conspicuously smooth and glossy, sparsely faveolated; main branches unpigmented, side branches ± variegated with bands of black pigment. Compressed morphotypes with thick, clawed, dark pigmented side branches occurring (as in U. perpusilla). Cortex annulations occurring. No papillae. Fibrils very rare. Medulla dense. Axis thick, occupying (34)–53–(71) % of branch diameter. Soredia and isidiomorphs unknown. Apothecia frequent, subterminal, rarely terminal, occasionally in series; cupular, getting mostly flat or undulate with maturity. Disc light yellow to brownish sometimes with black blotches or shaded; excipulum smooth, margin thin, often excluded, with few rays. Usneoid ascospores 8/ascus, simple, ellipsoid, hyaline, with no taxonomic value. Photobiont trebouxioid. Secondary chemistry (TLC): inconsistent hypostrepsilic acid chemosyndrome (Elix et al. 2007).
Usnea pallidocarpa belongs to a small group of polar-alpine species formerly summarized in the subgenus Neuropogon (Walker, 1985; Wirtz et al., 2008). This group is characterized by its fruticose growth form, a yellow-green thallus with varying black pigmentation, a black or rarely brown apothecial disc and saxicolous habitat (Walker, 1985). The new species (referred to as U. aff. perpusilla in Wirtz et al. 2006 and as Usnea sp. 1 in Wirtz et al., 2008) is closely related to U. perpusilla, but is distinguished by its smooth almost glossy thallus surface, a thick central cord, a dense medulla and a yellow apothecial disc with a smooth excipulum. Given just the single collection of the species and having not collected at sites with similar habitats in the near surroundings, especially north of Sán Carlos de Bariloche, it is very likely that the species occurs more frequently in the Andean Cordillera. However, we were unable to find U. pallidocarpa and U. perpusilla about 1000 km further south in the El Chalten region in Santa Cruz.
The epithet refers to the pale apothecial discs.
Known from just a single locality in the Andean Cordillera in southern South America (Argentina). It is an alpine species found at high altitudes about 1800 m on rocks, in communities with U. perpusilla, U. sphacelata and U. lambii.
Type:—ARGENTINA: Río Negro: Sán Carlos de Bariloche, Cerro Catedral; 41°16’S, 71°20’W, 1900 m; Dec 2003, Wirtz & Messuti PA-25b (holotype F).
Additional specimens examined (paratypes):—ARGENTINA: Río Negro: Sán Carlos de Bariloche, Cerro Catedral; 41°16’S, 71°20’W, 1850 m; Dec 2003, Wirtz & Messuti PA-24 (F).
A Usnea perpusilla ascomatis croceo-brunneis vel brunneis differt.