Similar to R. reductum but with a grey thallus and ±sessile apothecia often with blue-green pigment in the epihymenium and a ± hyaline exciple with a large, heavily pigmented, blue-green ‘cap’.
Type: Falkland Islands, Weddell Island: Circum Peak, summit, 51.927272°S, 60.925263°W, 205 m, pebbles, 23 January 2015, Fryday 10845 (MSC—holotype).
Description
Thallus pale grey, effuse, thin, c. 120–150 µm thick, usually with a wide black, fimbriate hypothallus, rimose to cracked-areolate, usually continuous but sometimes reduced to scattered areoles on a black hypothallus; rarely with the thallus absent and apothecia occurring directly on the hypothallus; cortical cells pale brown, c. 5 µm diam. overlain by a thin epinecral layer c. 10 µm high; medulla poorly developed with the photobiont layer reaching almost to the substrate, I–. Photobiont trebouxioid; cells 8–12(–15) µm diam.
Apothecia frequent, black, lecideine, sessile, 0.4–0.6 mm diam.; disc concave, becoming flat or slightly convex when over mature, margin thick, up to 0.1 mm wide, raised and persistent. In section:proper exciple brown, composed of ±vertically aligned hyphae c. 5 µm wide, with a dark blue-black (N+ red – cinereorufa-green) pigmented “cap”; this cap is often massively produced, 80–100 µm wide (Fig. 12B) with a much reduced or ± absent proper exciple below. Hymenium 85–100–150 µm high; paraphyses very thin, c. 1 µm wide, branched and anastomosing, swelling gradually to 3 µm at the apices, upper 10 µm olivaceous or blue pigmented (K+ intensifying blue, N+ red – cinereorufa-green); epihymenium diffuse, olivaceous to blue (K+ intensifying blue, N+ red – cinereorufa-green). Hypothecium dark brown. Asci narrowly clavate, Rhizocarpon-type, 75–85 × 30–35 µm; ascospores submuriform (rarely more than one primary longitudinal septum but with 3–5(–6) longitudinal septa), becoming pigmented when over mature, (20–)22.80±2.44(–35) × (9–)10.20±0.83(–11) µm; l/b ratio (1.91–)2.24±0.21(–2.64), (n = 20).
Conidiomata not observed.
Chemistry. K+ yellow, C–, Pd+ orange; stictic acid and norstictic acid (trace) detected by TLC.
Etymology. Derived from Islas Malvinas, the Spanish name for the Falkland Islands.
Ecology and Distribution. Apparently endemic to the Falkland Islands where it is common on siliceous rocks, especially at mid to high elevations. It is not present among the c. 10,000 collections in MSC made by Imshaug and co-workers from southern South America (Fryday & Prather 2001). Associated species: Buellia anisomera Vain., B. russa (Hue) Darb., Fuscidea asbolodes (Nyl.) Hertel & V. Wirth, Lecanora capistrata (Darb.) Zahlbr., Lecidea sp., Myriospora smaragdula (Wahlenb.) Nägeli, Poeltidea perusta (Nyl.) Hertel & Hafellner, Porpidia crustulata (Ach.) Hertel & Knoph, P. tuberculosa (Sm.) Hertel & Knoph, Rhizocarpon distinctum Th. Fr., R. nidificum (Hue) Darb. and R. simillimum (Anzi) Lettau.