Micarea subviridescens

Thallus pale grey-green to bluish grey-green, leprose, of thinly scattered to usually densely aggregated, ± globose goniocysts; goniocysts 12–18 µm diam., sometimes coalescing to form granules 25–45 µm diam., densely packed with coarse crystals that are not soluble in K; some outer hyphae coated by greenish, K± violet pigment; photobiont cells 4–7 µm diam. Apothecia 0.1–0.4 mm diam., to 0.6 mm if tuberculate, convex to subglobose or tuberculate, immarginate, whitish, pale to dark grey, brownish grey, or blackish; true exciple poorly developed; epithecium colourless, dull straw and K– or dull greenish and K± violet; hymenium 45–70 µm tall; hypothecium colourless to dull yellowish; paraphyses 0.5–1 µm diam., to 1.5 µm diam. towards the apices, rather scanty, branched. Asci 45–60 × 10–14 µm. Ascospores 10–18 × 4–6 µm, ovoid-ellipsoidal to cylindrical, (0-)1- to 3-septate. Pycnidia not seen. Thallus and apothecia Pd–, K–, C–, UV+ bright blue-white (the greenish pigment is C± violet, K± violet, N± red) (prasinic acid by TLC).

Differs from Micarea micrococca s.l. and M. prasina in the thallus having a slightly bluish tinge and the somewhat taller hymenium, and larger asci and ascospores; easily separated from these species by the very bright blue-white fluorescence, combined with the bluish grey-green leprose thallus and the terricolous habitat. The fluorescence is so bright that this lichen can be located by scanning likely habitat with a UV torch. When sterile, it can also be mistaken for a Lepraria species (especially L. elobata).