Frutidella caesioatra

Thallus crustose, rather thick, strongly warted-papillate, with dense subglobose, ± isidioid granules 0.1–0.2 mm diam., grey to dark grey or almost black, whitish when eroded; prothallus absent; photobiont chlorococcoid, cells 6–12 µm diam. Apothecia frequent, subglobose to ± hemispherical, sometimes tuberculate, sessile, often partly hidden by thallus granules, (0.3–) 0.5–1 (–1.2) mm diam., bluish black or with blue-grey pruina especially when wet; true exciple well-developed, not carbonised, colourless or with the outer parts dull yellowish, of radiating conglutinated hyphae (in K) ca 1.5-2 µm diam.; epithecium and upper part of the hymenium bright blue-green, K–; hymenium 50–65 (–75) µm tall; hypothecium ± colourless to reddish brown or almost violet, K+ reddish orange; paraphyses 1.3–1.8 µm diam., sparsely branched, sometimes anastomosing, apices not markedly swollen but with individual colourless gel coats. Asci 8-spored, 50–60 × 15–20 µm, elongate-clavate, with a broad, K/I+ blue, apical cushion. Ascospores aseptate, (11–) 15–19 (–26) × 5–7 (–9) µm, ellipsoidal, colourless, without a perispore. Pycnidia occasional, immersed or half immersed, globose or pear-shaped with pigmented apices; conidia filiform, 15–25 × 0.7–1 µm. Thallus C–, Pd–, UV+ blue-white (sphaerophorin, thiophanic acid and occasionally isoarthothelin and asemone).

Sometimes mistaken for Micarea assimilata and M. incrassata, which have apothecia without a bluish-pruinose bloom, smaller photobiont cells (4–7 µm diam.), and have thalli which are UV–.