Placopsis cribellans
≡Lecanora cribellans Nyl., Lich. Jap.: 42 (1890).
Description : Flora (1985: 401).
Chemistry : Thallus K−, C+ red, KC+ red, Pd−; containing gyrophoric acid.
N: South Auckland (Te Aroha), Wellington. S: Nelson (Mt Arthur, Lake Rotoiti, Mt Trovatore Lewis Pass), Westland (Kelly's Creek), Canterbury (Arthur's Pass, Cass, Port Hills Christchurch), Otago (Harbour Cone Otago Peninsula, Tautuku Bay Catlins), Southland (West Dome, Upper Oreti Valley, Deep Cove Doubtful Sound, Lake Monowai, Pahia Point, Invercargill, Bluff Hill). St: C: (Mt Honey, Beeman Hill, Mt Dumas). Colonising smooth, hard rock faces along roadsides, exposed boulders in rockslides, boulders in streambeds and along lakeshores, and also on coastal rocks throughout its range; also on bitumen pavement in Invercargill and possibly elsewhere. It appears to be readily distributed by fragmented isidia and quite commonly intact colonies of P. cribellans are surrounded by swards or scattered spots of detached isidia. Associating on coastal rocks with: Caloplaca circumlutosa, Carbonea phaeostoma, Pertusaria graphica, Psoroma melanizum, Rinodina thiomela and Verrucaria maura. At higher elevations associating with Rimularia psephota. Known also from the Aleutian Is, Alaska, British Columbia, Japan, Korea, Formosa, Chile, Juan Fernandez, Tierra del Fuego, The Galapagos, Hawai'i and Australia (Lamb 1947; Weber 1966; Brodo et al. 1987; Smith 1991; Filson 1996; Elix & McCarthy 1998; Galloway 2002d).
Circum-Pacific
Illustrations : Lamb (1947: pl. VII, figs 24, 25);
Placopsis cribellans is characterised by: rather small, neat, rosette-forming to spreading, closely appressed thalli, 1–3(–5) cm diam., often coalescing to form large colonies 12–15 cm across; convex lobes, 0.5–1.5 mm wide and 0.5–2.5(–4) mm long, contiguous, separated by narrow cracks; prothallus absent; a pale-green to green-brown upper surface when wet, grey-white to fawnish to grey-brown when dry usually darkening towards apices of lobes, with occasional to frequent, scattered white maculae (×10 lens) best seen when wet, smooth, shining to matt, frequently pitted-punctate with minute scars or depressions from abrading isidia, without soredia or pruina; isidia globose, 0.1 mm diam. or less, scattered to densely crowded, easily abraded and leaving whitish pits; solitary, sessile apothecia, 0.5–1(–1.5) mm diam., thalline margin persistent, entire, smooth, glossy concolorous with thallus, without isidia, discs subconcave to plane, smooth pale to dark red-brown, often densely white-pruinose; ascospores ellipsoidal, (12–)14–16.5(–17) × 6–9 μm. It is a rather variable species throughout its known geographical range and more work is needed on it to determine whether more than one taxon is involved. It is distinguished from P. subcribellans by the smaller, narrower, more convex lobes that are generally densely covered with globose isidia. On the other hand P. subcribellans has large, flatter thalli, with wider lobes separated by deep cracks from margins to centre.
