Hormonema Lagerb. & Melin, in Lagerberg, Lundberg & Melin, Svensk Skogsvårdsförening Tidskr. 25: 233 (1927).
Index Fungorum number: IF 8562; Facesoffungi number: FoF 11108, 6 morphological species (Species Fungorum 2022), 5 species with molecular data.
Saprobic or pathogenic on host. Sexual morph: Unknown. Asexual morph: Mycelium consisting of torulous, wide, often thick-walled, hyaline to dark olive to olive black, short cylindrical to subglobose cells, often with hyphal cells longitudinally septate, in age sometimes developing groups of muriform cells, generally sparsely branched, but sometimes becoming more branched with age. Conidiophores absent on mycelia. Conidiogenous cells holoblastic, integrated, intercalary, usually not differentiated from main axes of vegetative mycelium, occasionally arising from an undifferentiated lateral cell or filament, sometimes with a faint pore or slightly protruding annellate scar evident at the conidiogenous locus, often abundant along the entire radius of young extending hyphae, less so on older, contorted and melanized hyphae. Conidia aseptate, or rarely uniseptate in old cultures, usually ellipsoidal and tapered towards the base, but quite variable, occasionally pyriform or subglobose, smooth, often with one or more budding scars, hyaline to pale olivaceous-grey, often budding to produce 1 or 2 secondary conidia, accumulating in yeast-like masses along radial axes of vegetative hyphae (adapted from Bills et al. 2004).
Type species: Hormonema dematioides Lagerb. & Melin
Notes: Hormonema is characterised by torulous mycelium, holoblastic, integrated, intercalary conidiogenous cells and subglobose, smooth, hyaline to pale olivaceous-grey conidia. Hormonema comprises melanized filamentous taxa that produce slimy, yeast-like conidia that are produced basipetally in a non-synchronous way from one or few loci on cells of undifferentiated vegetative hyphae. Hormonema has been considered as the asexual morph of Sydowia polyspora (Thambugala et al. 2014; Rossman et al. 2015; Humphries et al. 2017). In the phylogenetic analysis of Hongsanan et al. (2020a), a putative strain of H. dematioides and Sydowia polyspora clustered together and hence they excluded Hormonema from Dothideaceae and transferred it to Dothideales genera incertae sedis. Hormonema resembles Aureobasidium in producing conidia synchronously from the conidiogenous loci but differs in having percurrent conidiogenous loci and different modes of conidiogenesis (Hermanides-Nijhof 1977; de Hoog and Yurlova 1994). Hermanides-Nijhof (1977) reported the likelihood of in vitro production of acervuli and pycnidia by Hormonema species. Hormonema differs from Rhizosphaera in that the latter has discreet, phialidic conidiogenous cells which arise intercalary or terminally on chains of cells from the pycnidial wall (Butin and Kehr 2000). Hormonema differs from Kabatina in that the latter has erect phialidic conidiogenous cells that form on the upper layer of a stroma-like acervulus (Sutton 1980). Hormonema can also be differentiated from Scleroconidioma in that the latter has an outer surface layer of stromatic conidiomata that form into conidiogenous cells and produce conidia through percurrently proliferating cells or phialides (Tsuneda et al. 2001). The taxonomic placement of Hormonema is uncertain and is in Dothideales genera incertae sedis. Fresh collections and sequence data of the type species is needed to confirm the taxonomic placement of Hormonema.