Jahnula Kirschst., Ann. mycol. 34(3): 196 (1936).
Saprobic on soft, decorticated woody material, predominately a freshwater genus, but also marine. Sexual morph: Ascomata immersed, semi-immersed or erumpent, sessile or attached to a long stalk, globose to subglobose, black, coriaceous, ostiolate, short-papillate, easily detached from the substratum, solitary or gregarious. Peridium comprising 3–5 layers of relatively large, thin-walled, brown or hyaline, angular cells, arranged in a textura angularis. Hamathecium comprising 2–4μm wide, hypha-like, filamentous, septate pseudoparaphyses, unbranched between the asci, branching and anastomosing above the asci. Asci 8-spored, bitunicate, fissitunicate, cylindrical or obclavate, pedicellate, thick-walled, with an ocular chamber and faint ring. Ascospores 1–3-seriate, ellipsoid-fusiform, pale brown to dark brown, 1- septate, constricted at the septum, guttulate, smooth or verruculose, some with mucilaginous appendages, pads or sheaths. Asexual morph: Unknown (Adapted from Hyde et al. 2013).
Type species: Jahnula aquatica (Kirschst.) Kirschst.
Notes: Jahnula was introduced by Kirschstein (1936) with J. aquatica as type species. Jahnula is characterized by immersed, semi-immersed or erumpent ascomata, cylindrical or obclavate asci, 1–3-seriate, ellipsoid-fusiform, pale brown to dark brown, 1- septate ascospores with mucilaginous appendages, pads or sheaths. Jahnula is polyphyletic with Jahnula sensu stricto accommodating J. aquatica, J. granulosa, J. potamophila and J. rostrata (Suetrong et al. 2011; Huang et al. 2018). Campbell et al. (2007) reported that Jahnula is paraphyletic in a combined analysis of LSU and SSU sequence data as Jahnula taxa grouped into three clades. Some species such as Brachiosphaera tropicalis and Speiropsis pedatospora clustered in Jahnula but they have not been synonymized until more Jahnula species are discovered (Suetrong et al. 2011). Campbell et al. (2007) and Suetrong et al. (2010) reported that other Jahnula species grouping in a separate clade might comprise other genera. Sivichai et al. (2011) mentioned that the anamorph of J. aquatica is Xylomyces chlamydosporus often found from freshwater habitats but without molecular confirmation and no further scrutiny of the different isolates used in the study has been carried out. Xylomyces is hence, considered as a synonym of Jahnula based on cultural studies but this needs confirmation from molecular data (Sivichai et al. 2011; McNeill et al. 2011). Suetrong et al. (2011) reported that Jahnula is polyphyletic based on a phylogeny of four loci namely ITS, SSU, LSU, and TEF-1. Jahnula is a polyphyletic genus in Aliquandostipitaceae and more taxa with molecular data are needed provide a stable phylogeny of the genus.