Thallus grey- to red-brown, moderately thick to thick (0.1-0.35 mm), cracked-areolate; areoles flat to convex, 0.2-1.0 mm diam.; medulla I–.
Anamorph: not known.
Teleomorph: ascomata apothecia, 0.6-1.0 (-1.2) mm diam., frequent, black, flat to slightly convex, sessile when well-developed, or innate among areoles. True exciple persistent, but often poorly formed, sometimes slightly crenate, composed of radiating, dark brown hyphae. Epithecium usually with aeruginose to blue-black pigment (macrocarpa-green; K–, N+ red), but occasionally brown (K–, N–). Hymenium 95-150 μm high. Hypothecium dark brown (arnoldiana-brown). Interascal tissue of cellular pseudoparaphyses, branched and anastomosing, 2.5-3.0 μm diam., swelling at the apex to ca 3.5 μm), with a sharply delimited, brown (atra-brown) cap. Asci 85-100 × 30-35 μm, clavate, fissitunicate, with a well-developed tholus that is K/I– in the lower part and K/I+ blue near the apex, lacking an ocular chamber, Rhizocarpon-type, 8-spored. Ascospores 21-25 × 8.5-12 μm, ovoid to ovoid-ellipsoidal, sometimes slightly curved, 1-septate, usually distinctly constricted at the ± supramedian septum, hyaline, becoming brown when over-mature, with a broad gelatinous sheath.
Chemistry: C–, K± yellow, Pd± orange. Stictic acid or no lichen substances detected by t.l.c.
Assessed by Woods & Coppins (2012) as of Least Concern.
Unlike other Rhizocarpon species with colourless, 1-septate ascospores, those of R. hochstetteri are large and often become pale brown with maturity. The medulla is I–, compared with the I+ blue medulla of R. richardii and R. polycarpum, with which it has sometimes been confused. Previous accounts included R. infernulum, which has smaller ascospores. Specimens containing stictic acid mostly occur at higher elevations.
SW and N England, Wales and Scotland. BLS map here.
On exposed, siliceous rocks, usually montane, sometimes lowland.