Polymeridium
Polymeridium (Müll. Arg.) R.C. Harris, in Tucker & Harris, Bryologist 83: 12 (1980).
Index Fungorum number: IF 4316; Facesoffungi number: FoF 08805, 50 morphological species (Species Fungorum 2022), 3 species with molecular data.
Lichenized on bark in terrestrial, chiefly lowland to lower montane tropical habitats, often in drier situations. Thallus usually ecorticate, rarely indistinctly corticate, whitish. Photobiont Trentepohlia. Sexual morph: Ascomata solitary to aggregate, erumpent to prominent, black, hemisphaerical to wart shaped or conical, carbonaceous, ostiolate, ostiole apical, rarely lateral or fused. Involucrellum carbonized. Excipulum prosoplectenchymatous, brownish to carbonized. Hamathecium paraphysoids, hyaline, straight, branched and anastomosing, embedded in a gelatinous matrix. Asci 4–8-spored, bitunicate, fissitunicate, clavate, short pedicellate, with a non-amyloid ocular chamber. Ascospores irregularly arranged to biseriate, fusiform ellipsoid, hyaline, multiseptateto rarely (sub-)muriform, with thin eusepta and rectangular lumina, smooth-walled, not or slightly constricted at the septa, often with a gelatinous sheath. Asexual morph: Pycnidia rare, immersed to erumpent, visible as black dots. Conidia aseptate, bacillar, hyaline. Chemistry: lichexanthone sometimes produced on thallus surface; ostiolar area or hamathecium rarely with anthraquinones (adapted from Aptroot & Lücking 2016).
Type species: Polymeridium contendens (Nyl.) R.C. Harris
Notes: Polymeridium is characterised by solitary to aggregate, erumpent to prominent, black ascomata, clavate, short pedicellate asci and fusiform ellipsoid, hyaline ascospores surrounded by a gelatinous sheath. The asexual morph is quite rare and characterised by immersed to erumpent, visible as black dots, and aseptate, bacillar, hyaline conidia. Polymeridium also produces lichexanthone on the thallus surface and the ostiolar area or hamathecium rarely have anthraquinones. Aptroot and Lücking (2016) provided an updated account of Polymeridium with descriptions, type citations and full synonymy for all species of the genus and transferred one species to Dictyomeridium. Polymeridium differs from Dictyomeridium in having angular lumina and ascospores with reduced endospore while Dictyomeridium has transversely septate or submuriform ascospores, rarely muriform with apical ostioles. Polymeridium is morphologically and phylogenetically a distinct and well-defined genus in Trypetheliaceae. Molecular markers available include P. albocinereum (LSU, mtSSU), P. catapastum (LSU, mtSSU), P. proponens (LSU, mtSSU), P. subcinereum (ITS, mtSSU) and P. subvirescens (LSU).
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