Bacidina assulata

Thallus straw-coloured to bright green, composed of minute merged granules to form a thin scurfy uneven crust or small warts, rarely with the thallus disintegrated into fine, pale green thallus granules. Photobiont cells to 17 μm diam. Apothecia 0.2–0.7 mm diam., constricted at the base, variable in colour from whitish and flesh-coloured to beige, pinkish-buff, brownish to grey-brown and dark fuscous brown, the margin becoming excluded, concolorous, paler or darker than the disc. True exciple (30–) 40–60 (–70) μm thick, composed of radiating hyphae with 1–2 rows of cells of the outermost part with lumina widening to 5–7 μm; upper and outer part pinkish orange, brown, fuscous brown and then K– or K± pinkish to purplish or olive-brown, K± intensifying; hypothecium to 60 μm tall, colourless to ± straw-coloured. Hymenium (40–) 50–60 (–65) μm tall, colourless or sometimes with a ± pinkish to olive-brown, K− or K+ intensifying epithecium as well as vertical streaks; pigment confined to walls of paraphyses and asci. Paraphyses of two types: unbranched, 1·5–2 μm diam. with globose apical cells to 2.5 (–3) μm diam.; also irregular, stout, 3–4 μm diam., forked with pigmented globose to elongate apical cells to 6 μm diam. Asci cylindrical to narrowly clavate. Ascospores acicular, (25–) 30–38 (–40) × 1.2–1.5 μm, 3- to 5 (to 6)-septate, straight. Pycnidia pale throughout, ± immersed within the thallus warts, 0·15–0·3 mm diam. Conidia filiform, ± straight to slightly curved (usually in the upper half) or ± hooked, (25–) 35–55 (–62) × 1–1·2 μm, 3- to 6-septate. No substances detected by TLC.

This recently described species is likely to have been overlooked in the past. It differs from Bacidina neosquamulosa in the lack of a subsquamulose thallus and the shorter spores, and from B. caligans in its longer and only slightly curved to apically hooked conidia and lack of a granular (sorediate) thallus. Ekman (2023) reported one specimen where the thallus disintegrated into fine, pale green thallus granules, these forms can be seperated from B. caligans by their longer conidia. There were some soralia close to the apothecia of a New Forest specimen, but this had B. assulata type conidia and it was not clear if they were actually assocaited or not.