Thelidium pluvium
Description : Thallus pale grey-green to dark-brown, continuous to slightly cracked. Perithecia forming conical–hemispherical projections, 240–450(–500) μm diam., covered at apex by a layer of thallus, ostiole inconspicuous, not depressed. Involucrellum present, brown, K− or + darker brown or greenish brown, rather thin and poorly developed, present around upper half of exciple. Exciple 200–350 μm diam., wall 20–25 μm thick at sides and base, brown at apex, colourless below. Paraphyses absent. Periphyses present, to 40 × 2–3 μm. Asci clavate, 8-spored, 75–100 × 25– 30 μm, fissitunicate, wall thickened above when young, with an ocular chamber. Ascospores ellipsoidal, straight, colourless, 1-septate, slightly constricted at septum, smooth, without halo or appendages, sometimes with numerous oil droplets, (20–)23–36 × 9–16 μm.
Chemistry : TLC−, all reactions negative.
S: On acidic to slightly basic rocks such as calcareous sandstone, in stream beds and dripping rocks. Known also from Great Britain, Western Europe, Scandinavia, Taiwan and Tasmania (Orange 1991b; Purvis et al. 1992; Santesson 1993; Scholz 2000; Coppins 2002b; Aptroot 2003a; McCarthy 2003c, 2006; Santesson et al. 2004; Elvebakk & Bjerke 2006).
?Bipolar
Illustrations : Orange (1991b: 102, fig. 1; 103, fig. 2; 104, fig. 3).
Thelidium pluvium is characterised by: the saxicolous habit (periodically inundated rocks); the pale grey-green to dark-brown, smooth to cracked thallus; perithecia with a relatively thin involucrellum; and 1-septate ascospores, (20–)23–36 × 9– 16 μm.
