Verrucaria devensis  

Thallus crustose, superficial, pale grey, dull greenish grey, mid greyish brown or mid brown, smooth, ± subgelatinous, usually locally or extensively cracked. Prothallus white, non-fimbriate. Thallus margin continuous, smooth. Areoles 40–600 µm diam., containing 1–7 perithecia, the surface slightly convex or uneven; 40–70 µm thick away from perithecia, to 140 µm thick near perithecia. Thallus cells 3.5–6.5 x 3.5–5 µm, irregularly arranged or in weak vertical columns, air spaces between cells absent or very few. Surface photobiont-free, the cell walls with a dilute or moderately dense brown pigment. Epinecral layer absent or thin and indistinct, a dark basal layer present either locally or extensively. Photobiont cells 6.5–15 x 4.0–6.5 µm.
Anamorph: not known.
Teleomorph: ascomata perithecia, 120–210 µm diam., immersed in the thallus, forming very low projections which are too ill-defined to measure, the apex initially visible only by the ostiole which forms a grey dot ca 20 µm diam., later as a grey or black disc to 180 µm diam. Involucrellum conical at first, becoming very wide-spreading and confluent, forming the dark basal layer of the thallus; surface densely pigmented, below paler, with pigment largely confined to cell walls so that the cell outlines are often visible. Peridium colourless at sides and base. Interascal tissue of periphysoids 20–30 µm long. Asci 8-spored. Ascospores  (16–) 18.5–22 (–23) x (7.5–) 8.5–9.5 (–10.5) µm, (1.7–) 2.2–2.4 (–2.6) times as long as wide, cylindric-ellipsoidal, colourless.