Helicoma Corda, Icon. fung. (Prague) 1: 15 (1837)
Saprobic on woody substrata. Mycelium partly immersed, pale brown, septate, branched hyphae. Sexual morph: Ascomata superficial, solitary, sometimes clustered, gregarious, superficial, subglobose, oval to obovoid, with soft texture, dark brown, pale brown above, with a central papillate ostiole, rarely with setae. Setae up to 80 μm long, dark brown, tapering towards subacute apex, widest at base, septate. Peridium thick walled, composed of brown to reddish-brown cells of textura angularis. Hamathecium comprising numerous, filiform, septate, branched, hyaline pseudoparaphyses. Asci 8-spored, bitunicate, elongate to cylindric-clavate, thickened at apex, pedicellate. Ascospores 2–3-seriate, elongate-fusiform, subcylindrical, tapering towards subacute ends, up to 10- septate, not constricted at septum, hyaline, smooth-walled. Asexual morph: Conidiophores superficial, macronematous, crowded, erect, dark brown, septate, rarely branched, darkened and slightly constricted at septum. Conidiogenous cells monoblastic to polyblastic, sometimes branched at apex, brown to dark brown, smooth. Conidia tightly coiled 1–1½ times, conidial filament 6–9μm wide, hyaline to pale brown, tapering towards the flattened end with a basal scar, septate, slightly constricted at septum, smooth-walled (Adapted from Boonmee et al. 2014).
Type species: Helicoma muelleri Corda
Notes: The genus Helicoma was introduced by Corda (1837) with H. muelleri as type species. Helicoma is unique in having relatively short, erect, thick, dark brown, smooth conidiophores, holoblastic conidiogenous cells and helicoid, hyaline, thick-walled, brown to dark brown conidia developing from terminal, denticulate conidiophores (Goos 1986; Seifert et al. 2011; Boonmee et al. 2014). Several species of Helicoma have been linked to sexual taxa in Tubeufiaceae and the relationship are confusing (Tsui et al. 2006, 2007; Zhao et al. 2007; Boonmee et al. 2011; Boonmee et al. 2014). The sexual morph of Helicoma is described from Helicoma rugosa (BPI 1104599, dried culture: BER 12 80–4). The asexual morphs are known from Helicoma rugosa formed in cultures of Thaxteriella helicoma (JCM 2739 and UBCF 13877). Lu et al. (2018b) redefined the morphological concept of Helicoma and introduced 10 new species with two asexual taxa. The first asexual species is characterized by conidia that are acrogenous or acropleurogenous, helicoid, circinate, dry, tapering towards apex, truncate at the base, coiled 1¼–1¾ times, not becoming loose in water (Lu et al. 2018; Hongsanan et al. 2020a). Another one is characterized by conidiogenous cells that are intercalary, cylindrical, with denticles, arising laterally from the inferior part of conidiophores as tooth-like protrusions, and conidia are pleurogenous, helicoid, hygroscopic, tapering towards apex and rounded at tip, coiled 1½–5 times, becoming loosely coiled in water (Lu et al. 2018b). 57 species were accepted in Helicoma and 12 species were excluded (Lu et al. 2018b). A new species, H. Hydei was lately introduced by Liu et al. (2019). Helicoma is a distinct and well-supported genus in Tubeufiaceae.