TYPE. UNITED KINGDOM. Cambria, V.C. 48, Merioneth, Ganllywd, 23/7223, 100 m, siliceous rock wall at edge of damp woodland, A.M. Fryday 3007 (E, holotype).
Life form. Lichenized fungus.
Description. [Modified from Fryday 2002] Thallus crustose, thin, 0·05–0·08 mm thick, pale brown, smooth, rimose in center becoming thinner and areolate toward margins; areoles flat, 0·2–0·5 mm diam.; prothallus well-developed, black. Photobiont chlorococcoid alga; cells (6-)8-12(14) μm diam. Ascomata lecideine apothecia, sessile, (0.2-)0.3-0.5(-0.7) μm diam.; disk black; margin black, thin, persistent. Exciple of radiating hyphae, pale brown with dark brown, carbonaceous outer cells; hypothecium medium brown (Arnoldiana-brown); hymenium hyaline, I+ blue, 75–90 μm tall; epihymenium brown (K-, N-), rarely with additional blue pigment and then N+ red, not granular. Paraphyses ~1.5 μm thick swelling at apex to 3.0 μm with sharply delimited brown (Atra-brown) cap, branched and anastomosing, readily separating in K. Asci 60–70 x 25–28 μm, Rhizocarpon-type, 8-spored; ascospores hyaline, halonate, 2-celled, 17.5–19(–20) 8.5–11.0 μm. Conidiomata not reported.
Chemistry. Spot tests negative; no substances detected by TLC.
Substrate and habitat. Saxicolous on siliceous rocks in woodlands and forests.
Distribution. Europe and eastern North America; in North Carolina found in the Blue Ridge ecoregion.
Notes. Recent molecular evidence suggest that this is a distinct taxon and should be elevated to species (Möller 2021). The hyaline, 1-sepate spores and lax paraphyses with a strongly expanded, pigmented cap could cause this taxon to be mistaken for a species of Catillaria.
Literature
Fryday, A.M. (2002) A revision of the species of the Rhizocarpon hochstetteri group occurring in the British Isles. The Lichenologist34(6): 451-477 (original description).
Möller, E.J. (2021) Molecular phylogenetics and genus delimitation in the Rhizocarpaceae (lichenized ascomycetes) with focus on the Rhizocarpon hochstetteri-complex. Master Thesis, Biodiversity and Systematics, Natural History Museum, University of Oslo, Norway.