Distinguished from all other members of the genus by the placodioid thallus with a red-brown margin and lower surface.
Type: Falkland Islands, West Falkland, Port Howard, Mt Maria, between Freezer Rocks and Castle Rock, 51.613504°S, 59.576515°W, 325 m, stone run, 26 January 2015, Fryday 10894 (MSC—holotype).
Description
Thallus crustose-placodioid to subfruticose, white to pale grey, 4–6(–8) mm thick, composed of contiguous convex areoles, 0.4–1.0 mm across that, in well-developed specimens, are supported on short pseudopodetia 2–4 mm high and 0.1 mm thick; undersurface of placodioid margin red-brown, this pigment often extending to the edge of the upper surface; medulla I–. Soralia orbicular, discrete, arising from an areole that often forms a rounded margin 0.1 mm wide, rarely two or more becoming confluent; soredia granular, c. 0.05 mm diam., greenish when fresh, becoming pinkish cream with age. Primary photobiont Myrmecia?; cells (12–)15–20(–22) µm diam. with thick hyaline wall. Cephalodia frequent, grey, ±orbicular with shallow marginal lobes, often radially fissured, 1–2 mm across; secondary photobiontChroococcus?; cells pale brown/orange 10–15 µm diam., 3–4(–8) enclosed in a yellow sheath 20–25 µm across, groups of smaller yellow-brown cells 3–4 µm diam. also present but not definitely part of the symbiosis.
Apothecia poriform in thalline warts, 0.7–0.8 mm wide; ostiole pale, slightly depressed; internal cavity ±spherical, 140–160 µm diam. Hymenium I+ yellow, 120–130 µm high; paraphyses simple, thin 1–1.5 µm wide expanding at the apex to 5 µm. Hypothecium hyaline c. 30 µm high, composed of randomly orientated hyphae, well differentiated from the hymenium. Asci cylindrical, c. 150 × 25 µm; ascospores hyaline, 8/ascus (35–)40.75±4.17(–48) × (18–)21.4±1.88(–27) µm, l/b ratio (1.68–)1.91±0.18(–2.25), (n = 20), cell wall c. 1–1.5 µm thick.
Conidiomata not observed.
Chemistry. Cortex K– or K+ dilute orange; medulla K+ bright yellow; stictic acid, constictic acid, ±norstictic acid and unknown pigment by TLC.
Etymology. The name refers to the red-brown margin of the thallus.
Distribution and Ecology. Saxicolous on granitic rocks, usually in stone-runs or fell-fields. Frequent on the Falkland Islands and also known from Tierra del Fuego (Isla de los Estados and Isle Grande). Associated species: Ochrolechia antarctica (Müll. Arg.) Darb., Ramboldia petraeoides and Lepra macloviana.