Strigula subtilissima
≡Racoplaca subtilissima Fée, Essai crypt. ecorc.: xciv (1824).
Description : Thallus foliicolous, subcuticular, effigurate, rounded to irregular, 4–10(–15) mm diam., distinctly lobate, lobes anastomosing and partly confluent, separated by small, irregular interspaces, lobes 0.07–0.1 mm wide, bordered by a thin, black prothallus 10–20 μm wide; surface dark grey-green, glossy, very thin, 8–12 μm thick, dominated by photobiont layer. Photobiont Cephaleuros, cells rectangular or oblong, 8–12 × 4–7 μm, forming continuous radiating plates. Perithecia (0.25–)0.3–0.5 mm diam., 90–200 μm tall, convex to subconical, black or partly dark-green, matt to glossy. Involucrellum 25–40 μm thick, brownish black, covered in upper parts by a thin layer of photobiont-containing tissue. Exciple brown in upper parts, colourless below centrum. Centrum somewhat applanate, 150–350 × 70–180 μm. Paraphyses simple, 1–1.5 μm thick. Asci obclavate, 40–70 × 4–7 μm. Ascospores 8 per ascus, biseriate, (1–)3-septate, fusiform to bacillar, apices obtuse, not constricted at septa, 10–16 × 2–3 μm. Pycnidia numerous, 0.1–0.2 mm diam., convex, black, glossy. Macroconidia simple but with a strongly staining central cytoplasmic zone, bacillar to ellipsoidal, 4–7 × 2 μm. Microconidia not seen.
N: Northland (Ngaiotonga Saddle). First collected in New Zealand on 14.viii.1976 by the late John Bartlett (Sérusiaux 1998a: 152). Known also from Central America, South America, West Africa, Madagascar, Réunion, Sri Lanka, China, Thailand, Java, Philippines, Hawai'i, Cocos Is., Galapagos Is, New Caledonia, Western Samoa, and Australia (Santesson 1952; Lücking 1992; Farkas & Sipman 1997; Smith et al. 1997; Vězda et al. 1997; Elix & McCarthy 1998; Lücking & Kalb 2001; Wolseley et al. 2002; McCarthy 2003c, 2006; Rønhede et al. 2003).
Pantropical
Illustrations : Fée (1824: tab. II, fig. 5 – as Racoplaca subtilissima); Santesson (1952: 184, fig. 26); Lücking (1992: 46, fig. 11F, M); Thor et al. (2000: 48, fig. 6I).
Strigula subtilissima is characterised by: the foliicolous habit; a dark-green reticulate thallus; rather acute to conical perithecia; fusiform to bacillar ascospores, 10–16 × 2–3 μm; and macroconidia 4–7 × 2 μm.
