Differing from Trapelia coarctata in the smaller apothecia, up to 460 μm diam., and from all other sequenced species by the strongly deviating ITS sequence.
Type: Falkland Islands, West Falkland, North of Fox Bay, Chartres Farm, ‘Patricia Luxton Nature Reserve’, 51·72459°S, 59·98522°W, alt. 10 m, on rocks in stream, shortly above water, 30 January 2015, Orange 22626 (NMW.C.2015.005.178—holotype).
Description:
Thallus well developed, extensive, with a more or less entire margin, soon becoming discrete secondary areoles, pale grey to dull greenish grey to dull greenish brown, matt; cortex thin, poorly differentiated, of rounded cells c. 4–5 μm with dilute brown walls; epinecral layer absent or up to 8 μm thick, of colourless, amorphous cell remains. Prothallus whitish, sometimes visible.
Apothecia semi-immersed to sessile when mature, to 460 μm diam., margin dark greybrown, when young with irregular teeth the same colour as thallus, or more or less white pruinose; sometimes surrounded by a low, thin collar the same colour as the thallus; disc brown-black, rough. In section:exciple thin to relatively well developed, c. 20–40 μm thick, brown at the surface. Hypothecium colourless; epithecium dull brown. Hymenium c. 110–140 μm high; paraphyses branched above, c. 1·5–2·5 μm thick at middle of hymenium, weakly thickened to 3 μm wide at apices, but occasionally distinctly thickened to 6·5 μm wide. Asci c. 95–100 ×20–24 μm, with apical thickening when young, ascus wall and surrounding gel uniformly K/I+ dilute blue; ascospores 17–27 × 8–12 μm, 1·8–2·5 times as long as wide [39/2].
Conidiomata not detected.
Chemistry. Gyrophoric acid.
Etymology. From the Latin word ‘tristis’ (dull coloured), referring to the colour of the thallus of some specimens.
Ecology and distribution. On rocks beside streams, in the intermittently inundated zone, with Hydropunctaria sp., Xenolecia spadicomma and the moss Racomitrium lamprocarpum, rare; Falkland Islands.