Differing from Trapelia coarctata in the widely diverging ITS sequence, the presence of conidiomata and having 5-O-methylhiascic acid as the major secondary substance.
Type: Falkland Islands, East Falkland, Walker Creek Farm, 51·97722°S, 58·82197°W, on stones on bare stony soil, probably seasonally moist, 12 November 2015, Orange 23162 (NMW.C.2015.005.180—holotype).
Description:
Thallus diffuse, continuous or discontinuous, thin at margin; thin to locally well developed, cracked, sometimes into discrete secondary areoles, very pale pinkish grey, matt, faintly pruinose in places. Prothallus not seen.
Apothecia when emerging with the margin covered by thallus material, becoming very irregularly toothed, disc appearing early; sessile when mature, to 600 μm diam., pseudothalline margin often forming a ring around the disc, concolorous with thallus, often excluded later; disc more or less plane or slightly concave, brown to black, rough. In Section:Hypothecium colourless; hymenium c. 160 μm high. Ascospores 16·5–19·5× 8–14 μm, 1·3–2·2 times as long as wide [20/2].
Pycnidia immersed, appearing as grey dots or short lines 60–100 × 60–80 μm; conidia 12·5–20·5×0·8 μm, strongly curved.
Etymology. From the Latin word ‘sitiens’ (thirsty, dry, parched), referring to the habitat on rocks and stones which are only occasionally moist.
Ecology and distribution. On seasonally moist rocks and stones, with Myriospora smaragdula, Lecanora polytropa, Trapelia sp. J, Trapelia sp. M, T. placodioides and Xenolecia spadicomma; rare, Falkland Islands.