Flora of New Zealand Series

Thallus crustose, heteromerous, orbicular, rosette-forming to spreading, lobate at margins in some species, closely attached, saxicolous or terricolous. Upper surface corticate, cortex paraplectenchymatous, matt or shining, areolate-cracked or with irregularly anastomosing cracks or continuous, or warted or wrinkled-plicate, usually whitish or cream or pinkish, orange-red in some species, pale green or olive-brownish or blackened in others. Soredia and isidia present or absent. Photobiont green, Protococcus, cells spherical, 4-12 µm diam. Cephalodia always present, ± conspicuous, sessile or immersed, discoid or subglobose, irregularly lobed or folded and wrinkled, pinkish, reddish or red-brown or greyish, containing Nostoc, Stigonema or Scytonema. Apothecia sessile or immersed, lecanorine, with a thalline margin concolorous with thallus, proper margin present, pale (sometimes undeveloped), disc variously coloured, ± plane, smooth or minutely scabrid, sometimes cracked, matt or shining or white-pruinose. Hymenium 80-320 µm tall, colourless or pale yellowish. Epithecium sordid yellowish with small, yellowish granules also present on tips of paraphyses. Paraphyses 1.5-2 µm thick, discrete, slightly swollen at apices. Hypothecium colourless, or pale yellowish, of intricately interwoven, unorientated hyphae. Asci cylindrical to cylindrical-clavate, 8-spored. Ascospores uniseriate or subbiseriate, colourless, simple, ellipsoid, elongate-ellipsoid or subfusiform. Pycnidia immersed, minute, punctiform.

Placopsis is related to Lecanora but is separated from it and treated as a distinct genus by the constant presence of cephalodia. It is placed close to Trapelia in the family Trapeliaceae. Species of Placopsis colonise acid rocks or soils, and many grow best in areas of high rainfall, particularly in stream or river beds on boulders or on gravels. In New Zealand species are most common in alpine areas, particularly in wetter, western parts, consolidating stream beds and glacial moraines, but some taxa range more widely and are found on coastal banks, and rocks. Of the 34 described species, most are found in the Southern Hemisphere [Lamb Lilloa 13: 151-288 (1947)] with 13 species recorded from New Zealand, 6 of which appear to be endemic. The genus is still however much in need of collection and study in New Zealand. Typification of taxa follows Lamb (loc. cit.) except where otherwise stated.