Like A. impressula, A. atrata has a thallus of contiguous areoles of usually uniform size. Acarospora atrata grows in full sun in exposed areas in mixed saxicolous lichen communities on a variety of rock types, including granite, schist, and iron-rich gneiss, and even on wood according to Magnusson (1929). It has been reported from Sweden, France, and central Europe at low elevations. In the Czech Republic it grows below 700 m. The species was submerged by Roux (2007) in synonymy with A. impressula and forgotten. The holotype in Paris is probably lost.
Acarospora atrata differs from A. impressula in having hemiamyloid (red or blue to red) vs. euamyloid (dark blue) hymenial gel in Lugol’s. It has the ellipsoid (cylindrical) ascospores vs. the broadly ellipsoid ascospores of A. impressula. Acarospora atrata has usually flat areoles under 1 mm in width while A. impressula usually has large areoles up to 2.5 mm wide, which are flat to subconvex. Future taxonomic work will probably discover and circumscribe several taxa in the morphological species concept of A. atrata. In Czech Republic probably both species are infrequent and under-collected.
Literature: Magnusson A.H. (1929): A monograph of the genus Acarospora. – Kungliga Svenska Vetenskaps-Akademiens Handlingar 7: 1–400. Roux C. (2007): Likenoj de Okcidenta Europo. Suplemento 4a: eltiraĵoj 2 (extraits 2). – Bull. Ass. Fr. Lichénologie 32: 5–36.taxonomic classification:
All records: 5, confirmed 2. One click on a selected square displays particular record(s), including their source(s).