TYPE: United States, Utah, Wayne, Ekker's Ranch, 1830 m, on dry sandstone, 5 19 1950, S. Flowers s.n. (UPS, holotype; ASU, ASUL000374, isotype).

Description. Hypothallus in substrate. Thallus an areolate crust, covering areas up to 10 cm, expanding through replication by division, areoles 0.2–2 mm wide, up to 600 µm thick, broadly attached to substrate. It has a flat topography until areoles become mature and swell, varying in height. Upper surface epruinose or lightly pruinose, without or with fissures, whitish when dry, gray-brown when wet. Epicortex 20–60 µm thick. Upper cortex 40–60 µm thick, irregular cells to 5 µm wide, upper layer red brown, lower layer hyaline. Algal layer 70–100 µm thick, continuous, except under apothecium, cells mostly 10 µm wide. Medulla 200–300 µm thick, gray, filled with substrate crystals, hyphae obscured, intricate 2–5 µm wide.  
Apothecia punctiform 0.1–0.4 mm wide, black looking, usually one per mature areole, but as many as eight in process of subdivision, with abundant fissures. Disc usually black when dry or wet, rough, immersed. Parathecium expanding around apothecium up to 30 µm, merging with cortex to sometimes form a raised thalline margin. Hymenium 100–170 µm tall, epihymenium reddish brown, ca. 20–30 µm tall, paraphyses 1–2 µm wide, apices unexpanded in gel cap with black pigment mark, hymenial gel IKI+ euamyloid (dark blue), epihymenium 20–30 IKI+ a distinctive light brown. Asci 90–100 × 18–21 µm. Ascospores 3–5 (–9) × 1.5 (–4) µm, variable [Magnusson (1952) reporting ascospores as 10–13 × 5 µm, see discussion below]. Subhymenium 10–20 µm tall, indistinct from base of hymenium, IKI+ blue. Hypothecium IKI-, indistinct from medulla. Pycnidia common on young areoles, a black dot, 180–200 × 60 µm (variable width), conidiogenous cells ca. 15 ×1 µm, conidia mostly 1 × 0.5 µm. 

Ecology and Distribution. Acarospora utahensis is a poorly known species occurring in Utah and Colorado with unverified reports from Idaho, Arizona and New Mexico: The species so far has been found on both calciferous and non-calciferous sandstone.  

Discussion. This species is easily identified by the euamyloid hymenial gel, high hymenium (usually 120–170 µm tall), variable ascospores 3–5 (–9) × 1.5 (–4) µm, and the white color formed by the thick epicortex. It looks like a member of A. strigata group.  
Ascospores examined from the holotype were observed to measure only 4–6.5 × 2–3.5 µm (Herre wrote on the outside of the packet that they were 4 µm wide). In the isotype no ascospores larger than 5 ×1.5 µm were observed. In the Poelt and Anderson collection from the Rocky Mountains in Colorado the longest mature ascospores seen were 8 × 2 µm.
In the Sonoran flora Acarospora utahensis was treated as a synonym of A. strigata, but euamyloid hymenial gel, useful for identification of the species, and molecular evidence support its recognition as a distinct species.

Literature

Magnusson, A. H. (1952). New crustaceous lichen species from North America. Acta Horti Gotoburgensis 19: 31–49.