Placopsis microphylla
≡Placopsis parellina f. microphylla I.M.Lamb, Lilloa 13: 249 (1947).
Description : Thallus closely attached to substratum, orbicular to diffusely spreading, 0.5–3(–7) cm diam., composed mainly of small, flattened, scattered to ±contiguous squamules, 0.4–1 mm diam., margins scalloped to crenulate, flattened to thickened and somewhat swollen, with a central white-pruinose spot, often brownish at edges, without a marginal prothallus. Upper surface pale-green to olive-green when wet, whitish grey to pale pinkish when dry, sometimes brownish-oxydated in older parts, convex to shallowly hummocky or undulate, continuous to distinctly areolate, areolae angular, separated by narrow to gaping cracks, white-pruinose in glistening patches (×10 lens), sorediate, without isidia, maculae or pseudocyphellae. Soralia excavate, 0.2–1 mm diam., at first with a sharply defined and slightly raised margin appearing vesicular-excavate and exposing the green sorediate interior, at length eroding large areas of thallus, sometimes forming a completely sorediate sward. Soredia granular, often coarse, pale grey-green or olive to lettuce-green. Cephalodia scattered, central, orbicular, (0.2–)1–3(–5) mm diam., sessile, convex, smooth to plicate-ridged to radially cracked, dark purple-blue when wet, yellow-brown to pinkish brown to rust-red when dry, epruinose. Apothecia rather rare, widely scattered, sessile, constricted at base, rounded, (0.1–)0.2–1(–1.2) mm diam., whitish at first with a granular-papillate to verrucose proper margin obscuring disc (appearing under ×10 lens as a small, white hotcross bun); thalline margin reduced to a collar of small granules concolorous with thallus; disc concave to ±plane, vivid candy-pink (when moist) to red-brown, white-pruinose when young, the pruina eroding with age; proper margin raised in a rim around and above disc, noticeably paler than disc, appearing papillate, whitish when young, translucent when moist, pale brown-pink when dry. Epithecium granular, pale olive-yellowish to pale-brownish, 16–36 μm thick. Hymenium colourless, 169–180 μm tall. Paraphyses simple, 2–3.5 μm diam., apices not thickened or moniliform. Hypothecium pale-yellow or pale-brownish, opaque, 160–215 μm thick. Asci cylindrical, (116–)120–140 × 15–18 μm. Ascospores uniseriate in ascus, broadly ellipsoidal, 21.5–27(–30) × 13.5–15 μm, contents granular, vacuolate, pinkish when fresh. Pycnidia scattered, immersed, mainly central, ostiole 0.08–0.12 mm diam., dark-brown, papillate to punctiform. Conidia filiform, straight or slightly curved, 8.5–11.5(–12) × 1 μm.
Chemistry : Thallus K−, C+ red, KC+ red, Pd−; containing gyrophoric acid.
N: Taranaki (Everett Road), Wellington. S: Nelson (Puponga, Upper Buller River), Canterbury (Dyer's Pass, Harry Ell Walkway, Victoria Park, Port Hills Christchurch). Otago (Poolburn Reservoir, Pomahaka River above Hukarere, Loganburn Reservoir, Dunedin Botanic Gardens), Southland (Cascade Creek, Eglinton Valley, Monowai, Blue Cliffs to Sandhill Point track). On damp, streamside and lake-shore rocks, often partially submerged, or on damp rock outcrops in grassland and on clay banks along well-used tracks and paths. Often showing a burst of growth in these disturbed soil sites over winter. Known also from southern South America (Lamb 1947; Galloway 2002d).
Austral
Illustration : Lamb (1947: pl. VIII, fig. 29 – as Placopsis parellina f. microphylla).
Placopsis microphylla is characterised by: small flattened squamules with a central white-pruinose spot; shallowly eroding, vesicular-excavate soralia, with a sharply defined and often elevated margin, exposing green, granular soredia; pale-pink apothecia with elevated papillae around margins. It is distinguished from P. argillacea by the smaller apothecia with a much thinner and narrower proper margin, rarely or never with a sorediate thalline margin, and a candy-pink disc, with a dusting of white pruina.
