Myriospora rufescens has small brown areoles (usually around 0.5 mm wide and rarely larger) growing in a contiguous or distinctly overcrowded thallus. The hymenium is (60–)80–120(–140) µm high and hemiamyloid (IKI+ red or blue to red). Apothecia are 0.2–0.4 mm wide. A diagnostic character is the elevated apothecia in a black parathecial crown that is 25–40 µm wide. Unlike other Myriospora, it may be hard to identify to genus because hymenium is below 140 µm, the algal layer is not totally interrupted and a microscopic section may be interrupted or not. It is similar to Acarospora fusca but differs especially in having the black parathecial crown and continuous thallus.
The species occurs on sandstone and other siliceous rock usually in full sun at low elevations probably below 600 m. Its center of distribution is apparently in the United Kingdom where it is frequent especially on anthropogenic substrates, such as monuments, gravestones, and tops of walls (Knudsen et al. 2021a). Myriospora rufescens is rare in the Czech Republic and was collected on pebbles in Soos National Nature Reserve in western Bohemia.
Literature: Knudsen K., Kocourková J., Cannon P., Coppins B. P., Fletcher A. & Simkin J. (2021a): Acarosporales: Acarosporaceae, including the genera Acarospora, Caeruleum, Myriospora, Pleopsidium, Sarcogyne and Trimmatothelopsis. – Revisions of British and Irish Lichens 12: 1–25. Knudsen K., Kocourková J., Hodková E. & Schiefelbein U. (2021b): A new species of Myriospora (Acarosporaceae) and a report of Myriospora rufescens from central Europe. – Herzogia 34: 327–338.taxonomic classification: most frequented synonyms:Acarospora rufescens, Silobia rufescens
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