Helicosporium Nees, Syst. Pilze (Würzburg): 68 (1816) [1816-17].
Saprobic on leaves, bark, and twigs, or on stromata of Diatrype stigma, Diatrypaceae (Xylariales), on decorticated or decaying wood, in terrestrial habitats or submerged in freshwater, widespread in temperate to tropical regions. Sexual morph: Ascomata superficial, solitary, scattered, globose subglobose, bright yellow brown to yellow orange, collapsing when dry, darkened near ostiole. Peridium of several layers, composed of bright yellow cells of textura prismatica to angularis. Hamathecium comprising numerous, filiform, septate, branched, hyaline pseudoparaphyses. Asci 8-spored, bitunicate, cylindric-clavate, apedicellate, thickened at apex, with an acute ocular chamber. Ascospores biseriate, elongate fusiform, tapering towards narrowly subacute ends, trans-septate, hyaline. Asexual morph: hyphomycetous, helicosporous. Conidiophores macronematous, mononematous, setiferous, erect, septate, unbranched, dark brown, fertile in middle, sterile, tapering towards narrow subacute at apex, smooth walled, arising directly on substrate, from thick-walled, closely septate, recumbent hyphae, crowded or in fascicles, glistening, light coloured. Conidiogenous cells polyblastic, intercalary, rarely terminal, with lateral minute denticles each with single conidium. Conidia coiled 3½–4½ times, tightly to loosely coiled, rounded at apical end, truncate at base, hyaline, 7–13-septate, slightly constricted at septa, smooth-walled (Adapted from Boonmee et al. 2014).
Type species: Helicosporium vegetum Nees
Notes: Helicosporium was introduced by Nees (1817) with H. vegetum as type species. Linder (1929) redefined the generic concept of Helicosporium. Goos (1989) revised the status of Helicosporium and included species with hyaline conidia whose filaments do not exceed 3 μm diam. Helicosporium is characterized by bright yellow brown to yellow orange ascomata, formed on stromata of other fungi, elongate-fusiform ascospores, tapering towards narrowly subacute ends, trans-septate, hyaline, with hyaline, helicoid conidia and produced directly on small denticles on setiferous conidiophores which are terminally sterile. According to Boonmee et al. (2014), Helicosporium is polyphyletic within the family Tubeufiaceae and is closely related with Acanthostigma, Acanthostigmina and Tubeufia (Tsui and Berbee 2006; Tsui et al. 2006). Lu et al. (2018b) re-studied all Helicosporium species, redefined the generic concept and recognized 13 species and omitted 25 species from the genus.