Acrospermum Tode, Fung. mecklenb. sel. (Lüneburg) 1: 8 (1790).
Index Fungorum number: IF 54; Facesoffungi number: FoF 06381, 28 morphological species (Species Fungorum 2022), 8 species with molecular data.
Saprobic or epiphytic on herbaceous plants. Sexual morph: Ascomata solitary or in groups, superficial, club-shaped to conoid, erect, uni-locular, brown to blackish when dry, with a short stipe or sessile, flattened when dry, swelling when moist, ostiole large, apex rounded. Peridium in horizontal section comprising three layers, an outer layer comprising dark brown cells of textura angularis, a central thick layer, comprising pale brown tissue of gelatinized hyphae with elongated cells, and an inner layer comprising dense tissue of small, light brown cells. Hamathecium of narrow, long, pseudoparaphyses. Asci 8-spored, bitunicate, narrowly cylindrical, pedicellate, with an ocular chamber. Ascospores fasciculate, filiform, hyaline, multi-septate, almost as long as the asci, smooth-walled. Asexual morph: Hyphomycetous. Conidiophores micronematous, pale brown, septate, branched or un-branched. Conidiogenous cells holoblastic, sympodial with denticles, long cylindrical, pale brown, smooth-walled. Conidia cylindrical, long ellipsoid, pale yellow, 1–3-septate, apically rounded, smooth-walled (Adapted from Webster 1956 and Hyde et al. 2013).
Type species: Acrospermum compressum Tode
Notes: Acrospermum was introduced by Tode (1790) with A. compressum as type species. Acrospermum is characterized by superficial, club-shaped to conoid, erect, unilocular, brown to blackish ascomata, narrowly cylindrical, pedicellate asci and fasciculate, filiform, hyaline, multi-septate ascospores. Rehm (1887) treated Acrospermum in Hysteriales. Ellis and Everhart (1892) transferred Acrospermum from Hysteriales to the Hypocreales. Lindau (1896) erected Acrospermaceae to accommodate Acrospermum and accommodated the family tentatively in Hysteriales. Von Hohnel (1917) considered Acrospermum as a pyrenomycete and placed it in the Sordariaceae of the Sphaeriales. Riddle (1920) discussed the internal arrangement of the mature ascocarp in tainted paraffin pieces and reported that the genus was related to the Hypocreales based on similar texture and pigmentation. Clements and Shear (1931) agreed with Ellis and Everhart (1892) and Riddle (1920) and treated Acrospermum as a member of Hypocreales. Arnaud (1930) added a discomycetous group Caliciees closely related to Coryneliales and suggested that this group might be related to Acrospermum. Eriksson (1981) redescribed the type species A. compressum and another species A. graminum. Eriksson (1981) mentioned that asci of Acrospermum may comprise more than one wall layer that do not open by a jack-in-the-box mechanism. Brandiff (2018) discussed the development of the ascocarp of Acrospermum compressum highlighting on the origin of the ascocarp wall and ascigerous cavity, the initiation and growth of the asci, and the shape and structure of the ostiolar opening. Acrospermum differs from Oomyces in that the latter has brightly colored ascomata which often unified to form a stroma comprising more than one locule while Acrospermum has clubbed shaped unilocular ascomata that vary in colour from bright yellows to black. (Eriksson 1981). Several authors added new species to Acrospermum (Minter et al. 2007; Hyde et al. 2018; Sundue et al. 2019). Acrospermum is morphologically and phylogenetically a distinct and type genus of Acrospermaceae. Molecular markers available for Acrospermum include A. adeanum (LSU, SSU, ITS, RPB2), A. compressum (LSU, SSU, ITS, RPB2), A. gramineum (LSU, SSU, ITS, RPB2), A. leucocephalum (LSU, SSU, ITS) and A. longisporium (SSU, LSU).