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Acarospora rufescens

Ascomycota › Lecanoromycetes › Acarosporales › Acarosporaceae › Myriospora

Description

A dark-brown crust forming a mosaic of closely adjoining, angular areoles. Small, deeply concave apothecia are sunk into the areoles, with a dark, slightly raised rim. Current name in BLS and ITALIC: Myriospora rufescens.

Source: ITALIC — Acarospora rufescens

Chemistry

Cortex and medulla: K−, C−, KC−, P−, UV−. No characteristic lichen substances are reported.

Source: ITALIC — Acarospora rufescens

Habitat and Substrate

Occurs on sandstone and other siliceous surfaces, including monuments, gravestones and wall tops.

Source: ITALIC — Acarospora rufescens

Similar Species

Compare brown Myriospora species and Acarospora fuscata. Negative spot tests alone do not establish identification.

Sources: ITALIC; BLS identification revision

How to Identify

Use the Myriospora key and examine the algal layer and the margin of the apothecium in section.

Source: BLS identification revision

Important Links

ITALIC — description, chemistry and images

British Lichen Society — species account and British distribution

GBIF — taxonomy and global occurrence records

AFL — alphabetical photographic index (general resource)

Identification Bibliography

Knudsen, K., et al. (2021). Acarosporales: Acarosporaceae. Revisions of British and Irish Lichens, 12, 1–25.

Nimis, P. L., et al. ITALIC: The Information System on Italian Lichens. Online account: Acarospora rufescens.

For identification, use the relevant key and compare the microscopic characters and chemical reactions. Photographs alone may be insufficient for closely similar crustose species.

Myriospora rufescens (Turner ex Ach.) Hepp ex UlothThallus crustose, episubstratic, areolate, forming an extensive, smooth, even crust, dull to dark brown, becoming thinner towards the edge, the areoles contiguous, separated by cracks, angular, (0.3-)0.4-1(-1.5) mm wide, 0.2-0.4 mm thick, flat to concave. Epicortex absent or very thin; cortex 30-40 µm thick, the cells mostly c. 2 µm wide, brown in upper part, colourless in lower part; algal layer 80-100 µm thick, irregularly interrupted by 10-15 µm wide hyphal bundles; medulla 100-250 µm thick, continuous with attaching hyphae, mixed with substrate crystals. Apothecia 0.2-0.4 mm across, 1-2 per areole, immersed, with a black (brown when wet), deeply concave disc concolorous with or darker than thallus, and an entire, slightly raised, black prominent margin. Proper exciple 25-40 µm wide, colourless, but the uppermost cells with dark brown caps; epithecium 10-15 µm high, brown to dark red-brown; hymenium colourless, (60-)80-120(-140) µm high, the hymenial gel hemiamyloid, IKI+ red or blue turning to red; paraphyses simple to sparingly branched and anastomosing 1-1.5 μm thick, the apical cells hardly swollen, cylindrical to clavate; subhymenium 10-30 µm high, opaque, densely inspersed with oil droplets, IKI+ blue; hypothecium 20-35 µm high, IKI-. Asci 100-200-spored, clavate, the apical dome K/I-, 80-100 x 10-20 µm. Ascospores 1-celled, hyaline, ellipsoid, 3-4 x 1-1.5 μm. Photobiont chlorococcoid. Spot tests: cortex and medulla K-, C-, KC-, P-, UV-. Chemistry: without lichen substances.

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