Leioderma Nyl.
Thallus foliose, lobate, heteromerous, dorsiventral, ± orbicular to spreading, corticolous, loosely attached, without a prothallus. Lobes undulate, adjacent, cuneate or flabellate, often imbricate or dissected, to 6 mm wide, margins incised or variously notched and dissected or ± sublobulate or phyllidiate-lacerate or sorediate and ± sinuous, ascending. Upper surface dark bluish-green to grey-green when wet, pale grey-blue when dry, undulate, minutely roughened-scabrid to coarsely areolate-scabrid, with or without soredia, without maculae, isidia or pseudocyphellae. Photobiont blue-green, Scytonema. Upper cortex of 2-3 layers of ± isodiametric cells with hyphae perpendicular to upper surface. Lower cortex absent, Medulla white, of loosely woven, branching hyphae. Lower surface pale, occasionally bluish or greenish-black, ± densely rhizinate. Rhizines pale or blue-green, complex, entangled, to 3 mm long. Apothecia biatorine, proper margin pale, disc pale red-brown or pinkish to dark brown or blackened, matt, epruinose, never gyrose-contorted, scattered, laminal, sessile or subpedicellate. Ascospores 8 per ascus, colourless, ellipsoid, simple, uniseriate.
Leioderma is a Southern Hemisphere genus in the Pannariaceae known from New Zealand, Chile, Tasmania, Tristan da Cunha with occurrences in tropical islands of the Pacific and Indian Oceans. The genus was first described by Nylander [ Lich. N.Z.: 47-48 (1888)] from New Zealand material of L. pycnophorum, and although the genus was not taken up after its description it seems that at least 5 taxa in the family Pannariaceae may be referable to it [Jørgensen Opera Bot. 45: 112 (1978)]. Santesson [ Ark. Bot. 31 A (7): 1-28 (1944)] describes the anatomy of L. pycnophorum and Keuck [ Biblthca lich. 6: 106-109 (1977)] the ontogeny. At least five species are present in the New Zealand flora which appears to be the centre of speciation in the genus. At present, two taxa await description. A detailed account of the genus is in preparation.
