Thallus not apparent, the ascomata developing in clusters on the thallus surface of its host lichens.
Anamorph: conidiomata not seen in the material studied.
Teleomorph: ascomata apothecia, lirellate, 150-260 x 130-200 µm, 100-150 µm tall, black, unbranched, rectangular to almost elliptical in outline, straight or slightly curved, not spreading at the base, the ends obtuse to almost truncate. Disc slit-like, not exposed; margin slightly turgid, rounded, the surface finely rugose, matt, epruinose. Excipulum 20-25 µm thick in the lateral part of the lirella, 25-30 µm in the basal portion, the cavity ± orbicular in section; wall composed of small irregular angular cells that are almost completely occluded by melanized material, except for the innermost layers. Epithecium poorly developed, the upper part of the paraphyses immersed in a pale brown gelatinous layer. Hypothecium poorly defined, the asci and paraphyses developing from a narrow pale brown basal layer of tissue. Interascal tissue composed of thick-walled paraphyses 2-2.5 µm diam., irregular and sparingly branched in the upper part. Asci 54-61 x 14-16.5 µm, cylindric-clavate, shortly stalked or almost sessile, very thick-walled, fissitunicate, the apex rounded and strongly thickened with a distinct apical cushion, 8-spored. Ascospores arranged biseriately, 18-20.5 x 5.5-6.5 µm, cylindrical to cylindric-ellipsoidal, sometimes very slightly clavate, the ends rounded, 3-septate, strongly constricted at the septa, hyaline but becoming dark brown and swelling somewhat when over-mature, smooth, with a gelatinous sheath to ca 2 µm thick surrounding young spores.
Not formally assessed, but considered to be of Least Concern by Coppins (ined.) The species has been recorded a number of times in recent years and is probably overlooked.
Similar to Opegrapha rupestris (found on thalli of Bagliettoa (Verrucaria) species) but that species usually forms only small clusters (<10) of relatively large lirellae (or occurring singly) which then may become widespread and eventually may become confluent. O. hochstetteri occurs as discrete clusters of minute lirellae. Lirellae in O. rupestris range up to ca 500 x 350 µm, but they are rarely much larger than ca 200 x 150 µm in O. hochstetteri. In O. rupestris the exciple is dull fuscous-olive brown in water, dull olive brown in K, red-purplish brown in N, while in O. hochstetteri it is fuscous brown with reddish tinge in water, distinct reddish-brown in K, fuscous brown in N.
Parasitic on thalli of Verrucaria hochstetteri and V. muralis.
Scattered throughout the British Isles.