Placopsis fuscidula
Description : Thallus closely attached, orbicular to spreading, 2–5(–7) cm diam., marginal lobes slightly swollen, 1–1.5 mm wide, and 1–4(–5) mm long, variously branched or divided, apices rounded to subcrenulate, ±flattened; centrally areolate, the areolae angular, 0.5–1.5(–2) mm diam., distinctly convex, separated by narrow to gaping cracks, without a prothallus. Upper surface pale greenish white or olivaceous when moist, pale-creamish, ivory to pale brownish pink or greyish blue when dry, smooth, matt or occasionally glossy at or near margins, commonly with a fine greyish to grey-white pruina (×10 lens) giving the surface a finely velvety appearance, without isidia, maculae, pseudocyphellae or soredia. Cephalodia scattered, sessile, 1–2.5 mm diam., rounded, smooth to plicate or radially cracked, dark purplish blue when wet, pale-pinkish to red-brown when dry, with or without apical, white pruina. Apothecia scattered, sessile, constricted at base, solitary or 2–3-together, rounded to subirregular through mutual pressure, 0.5–1.5(–2) mm diam. Thalline margin thick at first and almost obscuring disc, to ±excluded at maturity, concolorous with thallus, smooth, entire, thinly white-pruinose. Proper margin visible in mature fruits as a thin, entire to subcrenulate, raised margin, concolorous with or paler than disc. Disc concave at first becoming plane to subconvex, pale to dark red-brown, translucent when wet, matt, smooth to minutely papillate, with or without a fine, white pruina. Epithecium pale yellow- or pinkish-brown, granular, 20–25 μm thick. Hymenium colourless, (150–)170–200 (–225) μm tall. Hypothecium pale-yellowish, opaque, to 300 μm thick. Ascospores uniseriate in ascus, ellipsoidal, 17.5–22.5(–25) × (9–)10–12.5 μm. Pycnidia immersed in thallus, ostiole minute, punctiform, red-brown to black, often with a pale or whitish "halo" surrounding it. Conidia thread-like, curved to straight, 17–21 × 0.5–1 μm.
Chemistry : Thallus K−, C+ red, KC+ red, Pd−; containing gyrophoric acid (major), lecanoric acid and orsellinic acid (minor).
N: Wellington (Mt Ruapehu). S: Nelson (Denniston Plateau, Cobb Knob), Otago (Near Howden Hut, Lake Onslow), Southland (Mt Hodges, Dusky Sound). On subalpine rocks, and overgrowing bryophytes in grassland, associating with P. dennanensis, P. subgelida, P. salazina, Stereocaulon colenso. Known also from southern Chile, Juan Fernandez, Tristan da Cunha and Venezuela (Lamb 1947; Galloway 2002d: 89).
Austral
Illustrations : Lamb (1947: pl. IV, fig. 13; pl. VI, fig. 21 – as Placopsis chilena; pl. X, fig. 32).
Placopsis fuscidula is characterised by: closely attached, orbicular to spreading thalli, 2–5(–7) cm diam., marginal lobes slightly swollen, prothallus absent; a pale greenish white or olivaceous upper surrace when moist, pale-creamish, ivory to pale brownish pink or greyish blue when dry, smooth, matt or occasionally glossy at or near margins, commonly with a fine greyish to grey-white pruina (×10 lens) giving the surface a finely velvety appearance, without isidia, maculae, pseudocyphellae or soredia; scattered, sessile apothecia, solitary or 2–3-together, rounded to subirregular through mutual pressure, 0.5–1.5 (–2) mm diam., the thalline margin thick at first and almost obscuring disc, to ±excluded at maturity, concolorous with thallus, smooth, entire, thinly white-pruinose; the discs concave at first, becoming plane to subconvex, pale to dark red-brown, translucent when wet, matt, smooth to minutely papillate, with or without a fine, white pruina; a colourless hymenium, (150–)170–200(–225) μm tall; and ellipsoidal ascospores, 17.5–22.5(–25) × (9–)10–12.5 μm.
