Gyalideopsis crenulata

The thallus is very thin and continuous, forming an inconspicuous pale grey to brownish film on rock. Disc-like fruiting bodies (apothecia) are emergent, 0.2–0.3 mm in diameter, with a dark brown to black disc and a thick, dark, scalloped margin. In section, the uppermost pigmented layer (epihymenium) is red-brown, while the layer beneath the spore-bearing tissue (hypothecium) is colourless. The supporting threads (paraphyses) are very slender (about 1 μm wide) and interconnect (anastomose). The spore sacs (asci) are club-shaped, eight-spored, 55–75 × 15–25 μm. Spores are colourless, ellipsoid, 14–21.5 × 11–14.5 μm, with three cross-walls and one or two lengthwise walls (hence "submuriform"). No asexual propagules (pycnidia or hyphophores) were seen, and no lichen products were detected by chemical tests.^[2]

The species grows on small rock fragments (slate or pebbles) in copper-mining sites, although the particular stones on which it occurs do not themselves appear copper-rich. It has been recorded from two Welsh localities: the type site in Gwydir Forest (Caernarfonshire) and a second site at Eaglebrook Mine, Ceredigion (Cardiganshire). On the sampled fragments it occurred without other lichens, suggesting a narrow ecological niche in disturbed mine spoil.^[2] Gyalideopsis crenulata prefers flat stones lying on fine spoil material that provides damper conditions, typically occurring as isolated individuals with few associated species.^[3]