Thallus superficial, grey-green (in shade) to brown, 40–200 µm thick, at first composed of very small isodiametric granules 20–60 µm diam., increasing in size to form dorsiventrally flattened ± circular rosette-like patches with a minutely crenulate margin, these coalescing to form a diffuse crust which is uncracked or with has sparse secondary cracks; healthy layers of thallus often overlying older layers, which are partly dead or which contain abundant brown pigment. Surface of thallus minutely uneven. In section usually divided into units 30–80 µm diam. of ± isodiametric cells 4–10 x 3–6 µm in size, the walls thin or slightly thickened, 0.5–0.8 µm thick, cells at the surface (except in shade) with brown-pigmented walls. Prothallus absent. Photobiont cells 4–10 x 3.5–7.5 µm.
Anamorph: conidiomata pycnidia, rarely seen; conidia ca 5 x 1.2 µ in size.
Teleomorph: ascomata perithecia, forming projections 240–400 µm diam., often with an irregular covering of thallus below but exposed above, the ostiolar region often conspicuous, visible as a pale brown or whitish plane or convex dot 40–80 µm diam. Ascomata 180–305 µm diam., the peridium hyaline except for dilute brown pigment near the ostiole. Involucrellum variable, thin to well developed, often appressed to the peridium, or ± conical and extending down to the substratum. Asci clavate, I–, fissitunicate, the wall thickened above, ocular chamber usually present; dehiscence by extrusion of an endotunica to form a delicate rostrum, 8-spored. Ascospores arranged biseriately, (20.5–) 22.5–27 (–32) x (7.5–) 9–11 (–14) µm, length/breadth ratio (2.0–) 2.3–2.7 (–3.1), cylindric-ellipsoidal, mostly widest above the middle, hyaline, aseptate, thin-walled, gelatinous sheath and perispore absent.
Not formally assessed. The species was described by Orange (2013) as locally frequent in suitable habitats, and is probably under-recorded.
Reported to date from Wales (VC42 Brecon, VC43 Radnor, VC46 Cardigan, VC48 Meroneth and VC50 Denbigh), also from England (VC5 S Somerset) and Scotland (VC97 W Inverness).
On damp siliceous rocks and stones in or near streams, or on flushed ground.