Diagnosis. Similar to Acarospora americana but differing in having dark blue hymenial gel in Lugol’s (euamyloid), in having a continuous polysaccharide epicortex giving the areoles a dark shiny appearance, and in having a cortex of vertical hyphae.
TYPE: USA, Minnesota, Cook. Co., Superior National Forest, Caribou Rock Trail, on vertical east-facing side of Caribou Rock, 48.06380°N 90.45655°W, 560 m, on unknown crustose lichen and Aspicilia species and independent on diabase, 6 August 2017, P.A. Scott 5416 (Holotype, PRM!)
Etymology. Named in honour of the collector, citizen lichenologist Perry Scott, who collected the new species.
Description.Hypothallus endolithic, continuous with medulla, no algae observed, broadly and firmly attached or becoming loosely attached and squamulose, replicating by division. Thallus of areoles ≤1.3 mm wide, round to angular, flat to bullate, 300–500 μm thick, broadly attached, replicating by division. Upper surface dark brown, shiny, epruinose, black edged. Lower surface usually dark brown. Epicortex 5 μm thick, continuous. Cortex 30–50 μm thick, of distinct vertical hyphae, 2–3 μm wide, breaking up into irregular cells, terminating in expanded apices, 4–5 μm wide in dark brown gel cap, upper layer of cortex dark brown, c. 10 μm high, lower layer hyaline. Algal layer continuous without hyphal bundles, 50–100 μm thick, algal cells 10–15 μm wide. Medulla 150–300 μm thick, hyphae thin-walled, 2–3 μm diam. Apothecia usually 1 per areole, rarely 2 to 6, immersed ≤1 mm wide, the disc epruinose, rugulose, usually round. Parathecium indistinct or narrow to 15 μm wide, intergrading with cortex. Epihymenium 10–20 μm thick, coherent, brown to yellowish brown, sealed with polysaccharide hyaline layer c. 5 μm, a continuation of the epicortex. Hymenium (including epihymenium) 100–120(–150) μm tall, highest in bullate areole, hymenial gel IKI+ blue (euamyloid). Paraphyses 1.5–2 μm diam. at mid-level, apices expanded to 3 μm in pigment cap with blackish pigment mark, often with abundant oil drops. Asci 70–90 × (8–)10–12(–15) μm, narrow, c. 100 ascospores per ascus. Ascospores 3–4(–5) × 1.5–2 μm. Subhymenium 30–50 μm thick, IKI+ blue (euamyloid). Hypothecium 10 um wide. Pycnidia not observed.