Porpidia hydrophila
Thallus continuous to irregularly finely areolate-cracked, rarely gaping between areoles, surface smooth, ± shiny, occasionally minutely wrinkled, creamy white to pale olivaceous white, pale greyish, sometimes tinged orange or brown. Medulla I–. Prothallus inconspicuous and pale, or dark between other lichens in mosaics.
Anamorph: conidiomata pycnidia, generally extremely abundant. Conidia (8.0-) 9.0-12.0 μm long.
Teleomorph: ascomata apothecia, (0.2-) 0.5-1.2 (-2.5) mm diam., round to irregular, scattered, immersed at first, soon becoming sessile. True exciple thick, prominent, crenulate, black, matt or shiny, with a dark cortex and a ± pale medulla. Disc flat to convex at maturity, subconcave to flat when young, black, matt or granular-roughened, occasionally white-pruinose, occasionally centrally papillate or with small irregular plugs of sterile tissue. Excipular hyphae 3-5 μm diam. Epithecium 12-25 μm thick, aeruginose. Hymenium (80-) 100-120 (-140) μm tall, blue-green in upper part. Ascospores (13.5-) 18-23 × (5.5-) 7-8 (-9.5) μm, ellipsoidal to fusiform-ellipsoidal, fairly thin-walled, hyaline.
Chemistry: medulla C–, K–, Pd– (lichen products not detected by TLC).
Assessed by Woods & Coppins (2012) as of Least Concern.
N & W British Isles; locally abundant, particularly in W Ireland. BLS map here.
On inundated siliceous rocks, by upland streams and lakes and in rain hollows.