Description.Hypothallus endosubstratal, IKI-, hyphae 3-4 µm, not associated with algae. Thallus of areoles 0.5–1 mm wide, 0.2–0.4 mm thick, flat to convex, contiguous or scattered, to 1 cm. Upper surface thickly white pruinose and fissured, to thinly pruinose and gray to reddish-brown, with few thin fissures, becoming abscission fissures, areoles replicating by division, or lacking any fissures. Lower surface narrow, corticate, brown. Epicortex thin, ca. 10 µm. Eucortex 16–30 µm, upper layer reddish brown, lower layer hyaline, cortical cells paraplectenchymatous, 2–4 µm. Algal layer continuous, 50–60 µm thick, algal cells 9–14 µm. Medulla 50–60 µm thick, hyphae 3–4 µm wide. Apothecia one to five per areole, immersed, punctiform to 0.3 (rarely to 0.5 mm) wide, disc black, epruinose. Parathecium of thin hyphae10–15 µm wide. Epihymenium reddish brown. Hymenium (60–)80–100 µm high, epihymenium 10 µm tall, hymenial gel IKI+ dark blue, paraphyses 1.5–2.5 µm, apices in gell caps to 4 µm wide. Asci 65–75 × 15–17 µm, ascospores 100 to 200 per ascus, globose to broadly ellipsoid 3–4(–5) × 2–3 µmm, variable. Subhymenium 20–50 µm, IKI+ dark blue. Hypothecium 10–15 µm thick. Pycnidia not seen.
Chemistry. All spot tests negative; no secondary metabolites detected.
Distribution and Ecology.Acarospora coloradiana is a poorly known species occurring in North America, on limestone, calciferous sandstone, and Utah’s red sandstone, described from Colorado, verified from Idaho [Rosentreter 2046 (H), Utah (L. St. Clair (BYC)] with one unverified report from Badlands National Park in South Dakota (WIS).
Discussion.Acarospora coloradiana, when densely pruinose, looks distinctly like a member of the Acarospora strigata-group. But when pruina is thin and the brown cortex is exposed the convex areoles have a distinctive phenotype. The species was described by Magnusson (1929) from a single collection from Colorado by H. Willey in the Vienna herbarium (W).
Acarospora coloradiana differs from A. peltastica Zahlbr. especially in having dark blue euamyloid hymenial gel, while A. peltastica has non-amyloid hymenial gel (usually blue to red or immediately red). It has a low hymenium [60-100 vs. usually 100–120(–170) µm tall] and usually smaller ascospores, globose to ellipsoid or broadly ellipsoid [3–4(–5) × 2–3 vs. (3–)4–7(–12) × (2–)2.5–3(–4) µm. Acarospora peltastica is the common member of A. strigata-group in southwestern North America. It was described from Palm Springs, California, in the Greater Sonoran Desert Region, and occurring at least in Arizona, Nevada, and Utah. Acarospora utahensis has dark blue amyloid gel like A. coloradiana but with a taller hymenium [120–150(–200) vs. (60–)80–100 µm] and larger ascospores [3–5 (–9) × 3–4(–5) × 2–3 µm].
Magnusson, A. H. (1929) A monograph of the genus Acarospora. Kungliga Svenska Vetenskaps-akademiens Handlingar, ser. 3, 7: 1–400.