Placopsis lambii
Description : Thallus rosette-forming, generally orbicular to somewhat irregularly spreading, closely attached from margins to centre, (1–)3–30(–40) mm diam., (200–)225–300(–375) μm thick, pale lettuce-green to grey-green or pale olive-green, apices tinged brownish when wet, pale-creamish to fawnish buff (darkening in high-alpine specimens), to greyish or greenish white, when dry, never rusty red centrally or elsewhere, sometimes developing small tufts of reddish Trentepholia between cracks of thallus centrally and/or folds and cracks of cephalodia (×10 lens), distinctly lobate at margins, ±areolate centrally, without a projecting, marginal prothallus. Additional young thalli sometimes developing on over-mature, central cephalodia, and spreading in a second thalline layer. Photobiont green, trebouxioid, cells spherical, 7–8.5 μm diam. Lobes discrete to contiguous at margins, 0.5–1.5(–2) mm diam., 1–4(–8) mm long, noticeably convex (especially in high-alpine specimens) to plane, separated by fine to deep cracks, areolate centrally, the areolae separated by fine to deep cracks, sometimes individual areolae widely separated as distinct islands at centre near old cephalodia., apices flat, not swollen or inrolled, rounded to slightly incised to minutely lobulate. Surface smooth to minutely pitted in places, matt to burnished or glossy (reminiscent of ivory), here and there minutely maculate (×10 lens – best seen in fresh, moist material), sorediate, without isidia, pruina, pseudocyphellae or pustules. Soralia round to irregular developing early on even very tiny thalli, 0.1–1.0 mm diam., occasionally coalescing to form larger structures (to 2 mm diam.), scattered to somewhat crowded and with a tendency to develop in concentric bands on the thallus, shallowly to deeply concave-excavate, with a pale, well-defined margin. Soredia coarsely granular, 20–32.5 μm diam., olive-green to brown-black when wet, dirty greenish or brownish black when dry (×10 lens). Cephalodia solitary and ±central in immature thalli, rarely more widely scattered, developing in a broad concentric band between margins and centre with a large, often confluent deeply lobed cephalodium at centre, round to irregularly rosette-forming, (0.05–)1–5(–8) mm diam., smoothly hemispherical at first, becoming radially fissured with deeply gaping cracks at maturity, pale grey-purple or bluish when wet, pale yellowish pink to pink or warm-ivory when dry, occasionally with small, irregular patches of glistening white pruina on both young and mature cephalodia; photobiont Scytonema, in chains, cells compressed, cylindrical to fabiform, 10–15 μm diam. Apothecia rare, but when present numerous, crowded, developed in concentric, ring-like zones between margins and centre, subimmersed at first then sessile, constricted at base, rounded to slightly contorted through mutual pressure, 0.2–1(–1.5) mm diam., thalline exciple entire, prominent at first, 0.2–0.3 mm thick, pale-creamish or fawnish, becoming much thinner to almost disappearing at maturity, then concolorous with thallus or paler to ±whitish, glossy at first, matt at maturity, never pruinose; proper exciple narrow, persistent, pale yellow-brown to pale red-brown, projecting slightly above thalline exciple; disc slightly concave at first, ±plane or irregular at maturity, noticeably roughened-papillate (×10 lens), pinkish to reddish when wet, dull red-brown when dry, epruinose or very lightly white-pruinose in immature discs. Epithecium densely granular, olive-brown, 15–25 μm thick, unchanged in K. Hymenium very pale pinkish to hyaline, 100–135(–140) μm tall. Hypothecium densely interwoven, brown-pink at base rose-pink in upper parts, 150–175 μm thick. Asci 8-spored, cylindrical, tapering at foot, contents appearing pinkish in fresh material, (100–)110–125(–135) × 12.5–15 μm. Ascospores uniseriate in ascus, broadly ellipsoidal with rounded to slightly pointed apices, contents minutely granular, commonly with 1 large (central) and several smaller, rose-coloured oil droplets, 15–16.5(–18.5) × 6.5–8.5 μm. Pycnidia rather rare, immersed in thallus at margins of central areolae, solitary or clustered in groups of 2–6, 180–250 μm diam., ostiole red-brown to blackened, flat to slightly sunken, the margins slightly puckered, pale-whitish. Conidia numerous, colourless, thread-like, 20–26.5 × 0.5 μm.
Chemistry : K−, C+ red, KC−; containing 5- O -methylhiascic acid, gyrophoric acid and hiascic acid (Moberg & Carlin 1996).
S: Nelson (Mt Arthur Ra., Lewis Pass), Canterbury (Phipps Peak, Arthur's Pass), Southland (Gertrude Valley, Borland Saddle, Cascade Creek). On rock outcrops and on small, water-worn stones and pebbles in alpine areas (800–1890 m) of high rainfall. Because of its small size, and the fact that it appears to grow in interlocking mosaics with other, more prominent species of Placopsis, it is easily overlooked. P. lambii associates with the following lichens: Placopsis clavifera, P. cribellans, P. elixii (Galloway 2001a), P. illita, P. perrugosa, (two additional species of Placopsis at present undescribed), Stereocaulon ramulosum, and Trentepohlia sp. Known also from western Europe, Sweden, Norway, Iceland, the Faeroes and Jan Mayen, and the United Kingdom (Wirth 1987, 1995a, 1995b; Purvis et al. 1992; Santesson 1993; Moberg & Carlin 1996) in the Northern Hemisphere. It is also present in Kenya and Tanzania in East Africa and Lesotho in South Africa (Moberg & Carlin 1999) and in Chile, from the Xth Region to the Beagle Channel (Galloway 2002d).
Cosmopolitan
Illustrations : Wirth (1987: 378; 1995b: 743); Moberg & Carlin (1996: 321, fig. 1B); Dobson (2000: 310; 2005: 346 – as Placopsis gelida); Brodo et al. (2001: 571, pl. 690).
Placopsis lambii is characterised by: small, closely attached rosettes, distinctly lobate at margins, ±areolate centrally; with scattered, laminal, excavate soralia sometimes arranged in concentric lines on the thallus, and containing dark-green to brown-black granular soredia; with hemispherical, plicate or rugose cephalodia containing Scytonema; and subimmersed to sessile apothecia, arranged in concentric rings on thallus, with persistent creamish to whitish thalline margins and pinkish to red-brown, distinctly roughened-papillate discs, which are white-pruinose only in immature fruits. The asci are 8-spored, the ascospores uniseriately arranged, 15–16.5(–18.5) × 6.5–8.5 μm. Variation in Northern Hemisphere populations of P. lambii is discussed by Moberg & Carlin (1996).
