Placopsis elixii
Holotype: New Zealand. South I. Otago: Mt Aspiring National Park, West Matukituki Valley, Big Creek, true-right bank, near DOC car park, on schist rocks in grazed pasture on banks of stream, 1200 m, 30.vii.2000, D.J. Galloway 2556 – CHR 533413. Isotype – OTA 054005.
Description : Thallus distinctly lobate at margins, ±crustose centrally, in spreading, irregular rosettes, 2–5(–8) cm diam., coalescing in extensive spreading patches to 25 cm diam., (150–)200–250(–300) μm thick, pale-greenish, olivaceous to brownish pink when wet, pale whitish cream to fawnish when dry, often markedly rusty orange-brown centrally, to more generally rusty orange-brown in exposed habitats, without a delimiting prothallus. Photobiont green, trebouxioid, cells spherical, 10–13 μm diam. Lobes discrete to contiguous at margins, imbricate to areolate centrally, (0.1–) 0.5–1(–2) mm wide, 5–10(–15) mm long, separated by fine cracks, shallowly concave, apices ±flat, not noticeably swollen or inrolled. Surface smooth to very shallowly wrinkled or punctate-impressed, to shallowly papillate centrally, glossy, especially towards margins, to matt, apices sometimes distinctively white-pruinose (×10 lens), pseudocyphellate, maculate, without isidia, pustules or soredia. Pseudocyphellae white, punctate to effigurate, sigmoid to branched, 0.2–1 mm diam., scattered, often most noticeable towards apices. Maculae frequent, resulting from photobiont layer being interrupted by distinct bands of colourless hyphae, minute, white, imparting a marbled appearance to thallus surface (×10 lens) best seen when wet. Cephalodia rather widely scattered centrally, sessile, round to irregularly rosette-forming, (0.5–)1–2(–3) mm diam., smooth, hemispherical at first, becoming flattened, radially fissured with gaping cracks at maturity, pale grey-purple or bluish when moist, whitish to pale-pinkish to rusty brown when dry, sometimes with glistening patches of white pruina centrally (×10 lens); cyanobiont Scytonema, in chains, cells compressed, cylindrical to ±fabiform, 12–15 μm diam. Apothecia sessile, constricted at base, widely scattered, rather sparse to clustered centrally, solitary to 2–3-confluent, round to subirregular, (0.5–)1–1.5 mm diam., thalline exciple entire, concolorous with thallus or paler, sometimes with patches of glistening white pruina (×10 lens); proper exciple persistent, pale yellow-brown to pale red-brown, entire at first to ±scalloped and projecting above thalline exciple at maturity; disc subconvex when moist, plane to shallowly concave when dry, red-brown, rust-red to brown-black, roughened-papillate, epruinose or lightly white-pruinose in immature fruits. Epithecium densely granular, orange-brown to red-brown, dissolving in K, 25–50 μm thick. Hymenium pale orange-brown in upper parts, pale pinkish brownish below, 200–250(–280) μm tall, inspersed with small, pinkish oil droplets, paraphyses slender, straight, to 2.5 μm wide, apices not noticeably thickened. Hypothecium densely interwoven, 90–120 μm thick, pale brown-pink or yellowish brown in an upper layer, paler in K, 50–70 μm thick, ±colourless below, inspersed with numerous pinkish or brownish large oil droplets. Asci 8-spored, cylindrical, tapering at foot, contents appearing pale-pinkish in fresh material, 175–200(–215) × 25–30 μm. Ascospores uniseriate in ascus, ellipsoidal to broadly ellipsoidal, apices rounded or pointed, with one large central, or two smaller polar vacuoles (contents pinkish to reddish), contents of rest of spore oily-granular, very pale pinkish, (30–)31.5–36.5(–40) × (8.5–)10–12(–13.5) μm; wall smooth, 1.5–2 μm thick. Pycnidia rather rare, sparse on central areolae, punctiform, red-brown to brown-black, 0.05 mm diam. or less. Conidia not seen.
Chemistry : Cortex K−; medulla K−, C+ red, KC+ pink, Pd−; containing gyrophoric acid.
S: Westland (Franz Josef Glacier, Fox Glacier, Waitaha River, Ivory Lake, Karangarua River, Paringa River, Haast River, Arawata River), Otago (Makarora River, Matukituki Valley, Routeburn Valley, Teviot River), Southland (Lyttles Flat, Hollyford Valley, Eglinton River). On streamside rocks, and in partially consolidated riverbeds on talus in high-rainfall areas close to and W of the Main Divide, from s.l. to 1240 m. Associating with other species of Placopsis, including P. cribellans, P. hertelii, P. illita, P. perrugosa, P. polycarpa, P. pruinosa.
Endemic
Illustration : Galloway (2001a: 51, fig. 1).
Placopsis elixii is characterised by: a spreading, rosette-forming thallus; distinctive, flattened, discrete marginal lobes that are often white-pruinose at the apices, and with scattered, effigurate to punctiform, white pseudocyphellae; a distinctively maculate upper surface (×10 lens); sessile cephalodia, hemispherical to ±flattened, rosette-forming containing Scytonema; sessile apothecia with persistent, whitish, entire margins, and rust-red to brown-black, mainly epruinose, distinctly roughened discs; a densely granular, orange-brown epithecium; and large, ellipsoid ascospores, (30–)31.5–36.5(–40) × (8.5–)10–12(–13.5) μm. Central parts of the thallus of some specimens are parasitised by a lichenicolous fungus, having scattered small, coal-black apothecia (to 0.1 mm diam.), with a brown hypothallus and epithecium, and cylindrical, colourless, simple ascospores, 10–13.5 × 1.5–2.5 μm. P. elixii is distinguished from P. perrugosa and from other rusty, orange-brown species occurring in New Zealand (P. bicolor (Tuck.) de Lesd., and P. lateritioides I.M.Lamb), by the laminal, white pseudocyphellae, the distinctive surface maculation, the patches of superficial glistening white pruina on lobe apices, and on the surface of cephalodia, and by differences in apothecial anatomy and ascospore size.
