Verrucaria aquatilis
Description : Thallus crustose, smooth, not cracked, dark-green to almost black, 20–40(–50) μm thick, becoming gelatinous when moist. Prothallus absent. Perithecia 0.13–0.26 mm diam., immersed, with only the ostiole evident. Involucrellum black, spreading, 30–60 μm thick, usually overgrown by a thalline layer. Exciple colourless. Ascospores broadly ellipsoidal to subglobose, 6–11 × 4.5–7 μm.
S: Otago (Canyon Creek Ahuriri Valley, Trotter's Gorge), Southland (Mataura River at Gore). On schist or greywacke stones or boulders at edge of streams and rivers; partially submerged. Sometimes associating with Rhizocarpon geminatum and V. fiordlandica. Also known from Great Britain, Europe, southern Siberia, and India (Zschacke 1934; Swinscow 1968: McCarthy & Johnson 1995).
Cosmopolitan
Illustrations : Zschacke (1934: 226, fig. 99); Swinscow (1968: 50, fig. 8); Dobson (2000: 404; 2005: 453).
Verrucaria aquatilis is characterised by: the saxicolous (aquatic rocks) habit; smooth, continuous, dark-green to black thallus; immersed perithecia; a colourless exciple; and ascospores 6–11 × 4.5–7 μm.
