Index Fungorum number: IF 10448; Facesoffungi number: FoF 12533, 17 morphological species (Species Fungorum 2022), 2 species with molecular data.
Colonies effused, thin to dense, velvety, grey, brown to black, saprobic on dead vegetation. Sexual morph: Unknown. Asexual morph: Mycelium superficial or partly superficial, partly immersed in the substrate, composed of brown, septate, branched hyphae bearing conidiophores. Conidiophores short, erect or repent, simple or branched, straight to geniculate, hyaline to dark brown. Conidia produced singly from broadly flattened tips of usually per currently proliferating conidiophores, muriform, in some species strongly compressed laterally, ovoid, curved or coiled, pale to dark brown, bearing globose to subglobose, 1 to many-celled secondary conidia (adapted from Penzig and Saccardo 1902).
Type species: Xenosporium mirabile Penz. & Sacc.
Notes: Xenosporium is characterised by grey, brown to black colonies, superficial or partly superficial mycelium, short, erect or repent, simple or branched conidiophores, and ovoid, curved or coiled, pale to dark brown conidia. Ellis (1963) reviewed Xenosporium. Pirozynski (1966) considered Xenosporium as morphologically similar to Xenosporella, transferred four known species of Xenosporella to Xenosporium and added a sixth species. Since then, several authors have added new species to Xenosporium (Deighton and Pirozynski 1966; Rao and Rao 1973; Panwar et al. 1973; Hughes 1978; Vittal 1981; Bussaban et al. 2003; Zhao et al. 2006). Linder (1929) reported that some species currently assigned to Xenosporium were accommodated in Helicoma. Linder (1929) recognized four species X. berkeleyi, X. larva, X. pleurococca and X. thaxteri and all of them were transferred to Xenosporium by Pirozynski (1966). Linder (1929) considered Acanthostigmella thaxteri Linder to be the teleomorph of X. thaxteri, but this was not confirmed by cultural studies and is doubtful. The conidial morphological concept of Xenosporium is quite broad with some species having dorsiventrally curved conidia (e.g. X. berkeleyi, X. larvale and X. pleurococcum) while others are nearly globose (e.g. X. shoranoorense) or ellipsoidal (e.g. X. africanum and X. boivinii). Xenosporium is unique in having conidia with longitudinal and cross septation, bearing secondary conidia. Subramanian and Sekar (1980) confirmed that Chaetosphaerulina yasudae Hino is the teleomorph of X. indicum based on single ascospore studies. The diagnostic characteristics of Xenosporium species are provided in Goos (1990) who reviewed Xenosporium. Molecular data is available for two species X. africanum (LSU, ITS, RPB2, TEF-1) and X. berkeleyi (GADPH) but lacking for the generic type. Kirk et al. (2013) and Wijayawardene et al. (2012, 2020) listed Xenosporium in Dothideomycetes genera incertae sedis. Fresh collections with DNA sequence data are needed to confirm the systematic position of Xenosporium.