A monograph of Helicogonium (= Myriogonium, Leotiales), a group of non-ascocarpous intrahymenial mycoparasites
The monotypic genus Helicogonium is revised, and Myriogonium is considered to be a later synonym. The type species of these genera are extraordinary simplified parasites in the hymenia of Basidiomycetes (Stereales), producing ascogenous hyphae and asci but no ascomata. Fifteen new species are described in the genus which all produce their asci among the paraphyses of inoperculate discomycetes (Leotiales). These partly or often entirely suppress the development of the host asci, thus simulating a single organism. Three taxa, Crocicreas gemmisporum, Olta biguttata (nom. inval.), and Orbilia rubinelta, are based on such dual organisms, representing Helicogonium gemmisporum (in Crocicreas helios), H. scrupulosae (in Olta scrupulosa), and H. orbiliarum (in Orbilia vinosa) respectively. For C. gemmisporum and O. rubinelta the lectotypification based on a single element is proposed. In most species of Helicogonium the ascospores are directly conidiogenous; the small conidia are often produced already within the living, premature asci. In several species an intrahymenial Coryne-like phialidic anamorph could be found in association with the teleomorph; in one species the phialides were also formed on short germ tubes arising from the ascospores of the teleomorph. Helicogonium is considered to belong to the Leotiales owing to its ascus characters: cylindric-clavate shape, hemispherical to conical, inoperculate apex with inamyloid apical dome of varying thickness (rarely unthickened), violent ascospore discharge. The closest relatives are seen in the mycotrophic, ascocarpous genus Gelatinopsis from which Helicogonium is believed to have evolved by retrogression.