Placopsis argillacea
≡Placodium argillaceum C.Knight, Trans. Linn. Soc. Bot. ser. 2, 1: 282 (1877).
≡Lecanora argillacea (C.Knight) Forssell, Bih. K. Sv. Vet.-Akad. Handl. 8 (3): 54 (1883).
≡Lecanora rhodomma var. argillacea (C.Knight) Hue, Nouv. Archs Mus. Hist. nat. Paris, sér. 3, 3: 59 (1891).
≡Lecanora rhodomma f. argillacea (C.Knight) Zahlbr., Cat. lich. univ. 5: 670 (1928).
=Placopsis rhodomma Nyl., Lich. Nov. Zel.: 56 (1888).
≡Lecanora rhodomma (Nyl.) Hue, Nouv. Archs Mus. Hist. nat. Paris, sér. 3, 3: 59 (1891).
≡Placodium rhodomma (Nyl.) Hellb., Bih. K. Sv. Vet.-Akad. Handl. 21(3/13): 59 (1896).
Holotype: New Zealand. Sine loco (prob. Wellington), on clay, 24.ix.1876, Charles Knight – WELT Herb Knight Vol. 31A: 17. Isotype – H-NYL 3648.
Placopsis rhodomma. Lectotype: New Zealand. Sine loco (prob. Wellington), 1867, Charles Knight 100 – H-NYL 23859 [fide Lamb (1947: 247)]. Isolectotype – WELT L 006273. Syntype – H-NYL 23858a.
Description : Thallus irregularly spreading in friable patches, 1–3(–5) cm diam., often coalescing in confluent swards to 10–15 cm diam., margins indeterminate to minutely plicate–crenate, or noticeably swollen when well-developed, and separating as small, independent squamules beyond parent thallus, without a prothallus. Upper surface plane to convex, hummocky, crowded-plicate to coarsely papillate (×10 lens), pale to dark greenish grey when moist, grey-white to white when dry, distinctly sorediate, here and there with small, round, white pseudocyphellae (best seen when moist), without isidia, maculae, or pruina. Soralia round to irregular, 0.2–1 mm diam., sometimes with a prominent, sharply defined, raised margin, soon spreading in confluent patches and at length obscuring thallus in granular, to pseudoisidiate, efflorescent, fresh lettuce-green (and contrasting with grey-green thallus) soredia when moist, pale grey-white when dry. Cephalodia scattered or in groups or lines, submarginal to laminal, sessile, projecting above level of thallus, (0.1–)0.5–1(–3) mm diam., rounded to contorted through mutual pressure, shallowly and rather delicately wrinkled–cerebriform, dark grey-purple when moist, brown-pink to pale-pink or whitish pink when dry, sometimes secondarily colonised by small, thalline squamules. Apothecia sessile, constricted at base, sparse to frequent (often not developed at all in strongly sorediate populations), scattered, solitary or crowded in groups, rounded or slightly contorted through mutual pressure, 0.5–1.5(–2) mm; disc concave to plane to subconvex, vivid-pink to red-brown, smooth to delicately wrinkled-papillate or roughened, sometimes also with a thin, white pruina; thalline margin, smooth, thick, well developed, to 0.1–0.3 mm diam., obscuring disc at first, concolorous with thallus, sometimes becoming granular-sorediate; proper margin prominent, thin, slightly raised above surface of disc, glossy, generally not obscured by thalline margin, concolorous with or slightly paler than disc. Epithecium pale brownish pink, granular, 15–30 μm thick. Hymenium colourless, not inspersed with oil droplets, 165–215 μm tall. Paraphyses slender, 1.5–2 μm diam., apices not swollen or moniliform. Hypothecium densely opaque, 120–180 μm thick. Asci cylindrical–clavate, (100–)110–135 × 12–15 μm, 8-spored. Ascospores uniseriate in ascus, broadly ellipsoidal, (14–)16–22 × 8–13.5 μm. Pycnidia and conidia not seen.
Chemistry : Thallus K−, C+ red, KC−, Pd−; containing gyrophoric acid.
N: Northland (Stephenson I., Little Barrier I., Great Barrier I., Kaipara North Head), South Auckland (Mt Maungatawhiri, Coromandel Peninsula, Motuhora I., Mangaotaki Valley near Pio Pio), Wellington (York Bay). S: Nelson (Maitai Valley), Marlborough (Wither Hills), Canterbury (Port Hills), Otago (Lake Wanaka, Poolburn Reservoir, Loganburn Reservoir, Pulpit Rock, Silver Peaks, Otago Heads, Allan's Beach, Portobello, Otago Peninsula, Dunedin, Wakari Road, Taieri Beach, S of Akatore Mouth, the Nuggets, Cannibal Bay). St: (Lonneker's Beach, Oban, Acker's Point, Broad Bay S of Port Pegasus). Ant.: C: (Tucker Cove). Locally common on steeply inclined to vertical clay banks, often with Gyalidea lecanorina and Stereocaulon ramulosum, coastal and inland.
Endemic
Exsiccati : Lojka (1886: Fasc. III No. 127); Vězda (1997h: 4, No. 340).
Illustration : Knight (1877: pl. 38, fig. 14 – as Placodium argillaceum).
Placopsis argillacea is characterised by: the pale to dark greenish grey to grey-white, effuse, granular-pulverulent, sorediate thallus, the thallus often totally obscured by a sorediate crust; the scattered, urceolate, flesh-coloured apothecial discs with thick, white sorediate margins; and broadly ellipsoidal ascospores, (14–)16–22 × 8–13.5 μm.
