Flora of New Zealand Series

≡Placopsis parellina f. ampliata I.M.Lamb, Lilloa 13: 251 (1947).

Holotype: New Zealand. Sine loco. Charles Knight – H-NYL 3644. Paratypes – BM, M.

Description : Thallus orbicular to irregularly spreading, closely attached from margins to centre, (5–)10–25(–35) mm diam., often forming mixed mosaics with other species of Placopsis, distinctly lobate at margins, subcrustose, areolate centrally. Lobes 0.5–1(–2) mm wide, and 2–4(–5) mm long, subconvex to plane, closely contiguous, separated by narrow cracks, to soon becoming areolate, shallowly scalloped or notched at margins, without a prothallus. Upper surface pale-greenish when moist, pale green-grey or grey-white to somewhat pinkish when dry, areolate, areolae angular, 0.2–0.8(–1) mm wide, closely contiguous to confluent, minutely uneven-lumpy, matt, minutely granular-roughened, rarely glossy, here and there with scattered, rounded, white pseudocyphellae, 0.1 mm diam., or less, or with a thin, somewhat eroded, white, patchy pruina; without isidia, maculae or soredia. Cephalodia scattered, mainly central, purplish blue when moist, pale-pink or yellow-brown when dry, 0.5–2(–3) mm diam., round to irregular, smooth and hemispherical at first, soon becoming shallowly wrinkled-plicate, at length fractured by deeply gaping cracks. Apothecia sessile, scattered, singly or in small groups (2–4), rounded or deformed through mutual pressure, (0.1–)0.5–1(–1.5) mm diam., disc markedly concave to plane, pale-pink to red-brown, generally white-pruinose; thalline margin prominent from the first, thick, concolorous with thallus, often obscuring disc and appearing thelotremoid; proper margin translucent, concolorous with or paler than disc, best seen when moist, generally obscured by thick thalline margin, sometimes prominent and then slightly glossy and raised above disc. Epithecium pale yellow-brown, 8–13 μm thick. Hymenium colourless, 150–195 μm tall. Asci cylindrical, 120–160 × 15–21 μm, walls 1.5–2.5 μm thick, apex to 7 μm thick. Ascospores broadly ellipsoidal, colourless, 20–22 × 11–12 μm.

Chemistry : Thallus K−, C+ red, KC−, Pd−; containing gyrophoric acid.

N: Wellington. S: Nelson (Kerr Bay Lake Rotoiti), Southland (Piano Flat Waikaia River). On streamside or lakeside rocks and on rocky riverbanks or old watercourses in full sunlight. It is very closely attached to the rock and is often extremely difficult to remove. Forming interlocking mosaics with Gyalidea lecanorina. Lobothallia radiosa, Placopsis illita, P. perrugosa, P. pruinosa, species of Porpidia and Stereocaulon.

Endemic

Illustration : Lamb (1947: pl. X, fig. 34 – as Placopsis parellina f. ampliata).

Placopsis ampliata is characterised by: an orbicular to spreading thallus, lobate at margins (without a prothallus), subcrustose, areolate centrally; a pale-greenish upper surface with scattered white pseudocyphellae, and a patchy, eroded, white pruina; sessile apothecia with prominent, thelotremoid thalline margins (often obscuring disc at first), and with pale-pink to red-brown, white-pruinose discs; and broadly ellipsoidal, colourless ascospores, 20–22 × 11–12 μm.