Thallus epiphytic on thin branches and twigs of paramo shrubs, foliose, up to 3 cm across, composed of 1–3 semicircular lobes per thallus; lobes 1–2 cm wide and 1–2 cm long, unbranched, light grey when fresh, with thickened, involute, grey margins, becoming white to pale yellowish grey in the herbarium. Upper surface glabrous except for a broad submarginal zone with appressed, arachnoid-byssoid tomentum; trichomes densely interwoven and irregularly arranged, 0.1–0.2 mm long and 5–6 µm thick at the base, composed of single hyphae; involute margin with underside minutely arachnoid; lower surface ecorticate, finely felty-arachnoid (representing the exposed medulla), white when fresh and becoming yellowish white in the herbarium. Thallus in section 250–400 µm thick, with upper cortex, photobiont layer, and medulla; upper cortex formed by a 50–100 µm thick layer of rather loosely woven, irregularly arranged, 4–6 µm thick hyphae supported by a 30–50 µm high 'medullary' layer of irregularly arranged to anticlinal, 4–6 µm thick hyphae, towards the margin no such distinction visible and the upper cortex entirely formed by loosely woven, irregularly arranged hyphae causing the tomentose appearance; photobiont layer 100–200 µm thick, irregular, composed of clusters of short, coiled cyanobacterial filaments wrapped in a dense, paraplectenchymatous hyphal sheath formed by jigsaw puzzle-shaped cells, clusters 30–50 µm diam., individual photobiont cells 10–12 µm broad and 6–8 µm long, dark blue-green to yellow-orange in upper portions, penetrated by tubular fungal hyphae; heterocysts sparse, hyaline to pale yellow, 8–10 µm wide and 5–6 µm long; cells of hyphal sheath wavy in lateral outline, 3–4 µm thick; medulla 30–50 µm thick, composed of loosely woven, irregularly arranged to more or less periclinal hyphae 4–5 µm thick; clamp connections not observed.
Hymenophore developed as irregular to elongate, resupinate patches dispersed on the underside, patches 1–3 mm long and 0.5–1 mm broad, with pale yellow, smooth surface and strongly involute, smooth margins; hymenophore in section 50–100 µm thick, composed of a paraplectenchymatous layer resting on loose, 4–6 µm thick, generative medullary hyphae and supporting the hymenium; hymenium composed of numerous, palisade-like basidioles and scattered basidia; basidioles 25–30 x 5–7 µm; basidia 25–35 x 5–8 µm, 4-sterigmate; basidiospores ellipsoid, non-septate, hyaline, 7–9 x 3–4 µm.
Chemistry: no substances detected by TLC.
Differing from the morphologically similar Cora hirsuta in the only marginally present, arachnoid tomentum and the epiphytic growth, and from the closely related C. inversa in the distinct upper tomentum and the absence of soredia.
Holotype:—COLOMBIA. Cundinamarca: Choachí, Páramo El Verjón; 4º 33' N, 74º 00' E; 3200 m; 18 August 2008, Lücking s.n. (F).
Genbank ITS barcoding sequence: DIC151
This is another new species with partially tomentose upper surface. It is most similar to Cora hirsuta (Lumbsch et al. 2011), which was found at the same locality, but differs in the nature of the tomentum, which is formed by erect trichomes of agglutinated hyphae in C. hirsuta and by an irregularly dissolved cortical layer of single hyphae in C. byssoidea. Also, whereas C. hirsuta has a glabrous submarginal zone, with the tomentum developed towards the center of the lobes, in C. byssoidea the tomentum is only seen close to the margin. The two species are actually not closely related and fall in two different clades within the genus (Dal-Forno et al. 2013). The sister species of C. byssoidea is C. inversa (see below), which differs markedly in its upper surface being glabrous and in the irregular lobe margins producing dark soredia.
This species is known from a single collection growing on a shrub in the Colombian paramo regions. Due to its small size, it is certainly overlooked.