Hypohelion P.R. Johnst., Mycotaxon 39: 221 (1990)
= Leptostroma Fr., Observ. mycol. (Havniae) 1: 196 (1815)
Leotiomycetes, Leotiomycetidae, Rhytismatales, Rhytismataceae
Saprobic on the host plant in terrestrial habitats, such as Arundinaria gigantea (Poaceae), Scirpus lacustris (Cyperaceae), S. validus, Stephanandra incisa (Rosaceae) (Sutton 1980, Wang et al. 2014) Sexual morph: see Grove (1937). Asexual morph: Conidiomata black, subepidermal, pycnidial, immersed, circular, occasionally elongated, unilocular, glabrous. Ostiole absent, dehiscence by irregular splits of overlying wall. Conidiomatal wall composed of 1-cell thick, dark brown cells of textura angularis or prismatica in the upper part, becoming thick-walled, dark brown to hyaline cells of textura angularis in the basal part. Conidiophores reduced to conidiogenous cells. Conidiogenous cells arising from inner layer cells of basal stroma, hyaline, holoblastic, sympodial to synchronous, filiform, integrated or discrete, indeterminate, smooth-walled, with several, unthickened conidiogenous loci towards the apices. Conidia hyaline, ellipsoid, unicellular, smooth-walled, eguttulate (adapted from Sutton 1980).
Type species: Hypohelion scirpinum (DC.) P.R. Johnst., Mycotaxon 39: 221 (1990)
= Leptostroma scirpinum Fr., Syst. mycol. (Lundae) 2(2): 598 (1823)
Notes: Leptostroma scirpinum (type of Leptostroma) was generally considered as the asexual morph of Hypohelion scirpinum by several authors (Grove 1937, Sutton 1980, Minter 1997). Johnston et al. (2014) regarded these two genera as taxonomically congeneric and recommended to use Hypohelion for the holomorph, because the latter name is well-established. The asexual morph of Hypohelion (= Leptostroma) is similar to Polystigma (= Polystigmina) in having holoblastic, sympodial to synchronous, indeterminate conidiogenous cells. However, Polystigma has filiform, hamate, tapered towards the apices, guttulate conidia, whereas Hypohelion has ellipsoid, eguttulate conidia (Sutton 1980, Dayarathne et al. 2017). There is no molecular data available for asexual morph of H. scirpinum (= L. scirpinum). To clarify the taxonomy of Hypohelion, many species will have to be recollected, and epitypified, so that authentic cultures and molecular data will become available to fix the genetic concept.
Distribution: Canada, China, Germany, Hungary, Latvia, Sweden, USA (Sutton 1980, Lantz et al. 2011, Wang et al. 2014).
Li WJ, McKenZie EHC, Liu JK, Bhat DJ, Dai DQ, Caporesi E, Tian Q, Maharachcikumbura SSN, Luo ZL, Shang QJ, Zhang JF, Tangthirasunun N, Karunarathna SC, Xu JC, Hyde KD (2020) Taxonomy and phylogeny of hyaline-spored coelomycetes. Fungal Diversity 100: pages279–801.