Citation: Pem D et al. (2019) Mycosphere Notes 275-324: A morphotaxonomic revision and typification of obscure Dothideomycetes genera (incertae sedis). Mycosphere 10(1), 1115–1246
Chionomyces Deighton & Piroz., Mycol. Pap. 128: 74 (1972)
Parasitic or epiphytic on the surface of living leaves. Sexual morph: Undetermined. Asexual morph: Colonies effuse, white, floccose. Mycelium hyperparasitic, consists of dark-brown to black, undulate, superficial, branched septate, thin and smooth-walled hyphae, thickly overgrowing superficial mycelium of leaf ascomycetes and bearing conidiophores as lateral branches. Conidiophores distributed singly or grouped onto loose fascicles, more or less erect, simple, colorless to pale brown, straight or flexuous with dense, refractive walls mainly towards the base, closely and markedly septate throughout or with the septa concentrated in the upper half, variable in length. Old conidial scars very slightly and evenly thickened. Conidiogenous cells holoblastic, percurrent, and sympodial. Conidia produced successively and holoblastically, one at a time from the tips of the conidiophores which proliferate percurrently by flipping the entire conidial scar to one side and growing through the opening to leave behind a series of pseudo-annellations, brown, fusiform, navicular or obclavate, attenuated towards the apex and often rostrate with a truncate unthickened hilum, 3 or more septate, smooth-walled. The conidia are firstly ovoid, then becoming elongate to produce a papillate apex. Mature conidia are spindle-shaped, colourless to brown, thin and smooth walled, 3–5 septate, with a wide truncate base and apical cell narrowing abruptly into beak-like projections, curved and wide at apex.
Type species – Chionomyces meliolicola (Cif.) Deighton & Piroz.
Notes – The genus Chionomyces was introduced for C. meliolicola by Deighton and Pirozynski (1972). The genus Chionomyces can be found on Amazonia, Irenopsis and Meliola spp. in tropical East and West Africa and in the Dominican Republic. Its sexual morph is so far unknown. Morphological characters defining the genus Chionomyces include dark-brown to black undulate, branched, septate mycelium, holoblastic, percurrent and sympodial conidiogenous cells with brown and fusiform conidia. Currently, seven species are accommodated in the genus Chionomyces (Index Fungorum 2019). Chionomyces meliolicola is distinguished from other species in the genus by having wider conidia (mostly 8–10 µm wide) which are 3–5 septate. Chionomyces was reported as the anamorph of the genus Melioliphila Speg. (1924) however, whether this association is correct is unresolved because sequences and cultures are unavailable. The specimen of Chionomyces meliolicola, collected from leaves of Meliola seyboensis is described below from PDD herbarium. It is not the type material, but it is typical of the species. The genus Chionomyces can be compared to Metacapnodium accommodated in Metacapnodiaceae wherein asexual morph occurs on subiculum and comprise hyphae with broad, dark brown cells, and chains of globose, moniliform cells, with strong constrictions at the septa. Based on morphological study alone, we could not accommodate the genus Chionomyces in any family and hence we retain it in Dothideomycetes genera incertae sedis. Fresh specimens are required and molecular data are essential to recognize its correct placement in Ascomycota.