MycoBank number:MB 58;Index Fungorum number:IF 58;Facesoffungi number: FoF 08102; 6 morphological species (Species Fungorum 2020), molecular data unavailable.

Type species –Actidium hysterioidesFr., Observ. mycol. (Havniae) 2: 353 (1818).

Notes – This genus was established by Fries (1823) to accommodateA.hysterioides, a stellate mytilinidioid fungus found onPinusandPiceain Europe, with two-celled, symmetric ascospores, light olive to reddish brown, later noted to be faintly longitudinally striate (Barr 1990a). Fries (1823) noted its similarity withGlonium. Zogg (1962) and Barr (1990b) recognised four species,A. hysterioides,A. baccarinii, both from Europe,A. pulchra, from China, andA. nitidum. Due to similarities in ascospore morphology,Actidiummay have affinities with other didymospored hysteriaceous genera (e.g. Actidiographium,GloniumandPsiloglonium), although molecular data are lacking.

Species