Radulidium Arzanlou, W. Gams & Crous, in Arzanlou et al., Stud. Mycol. 58: 89 (2007).
Index Fungorum number: IF 504566; Facesoffungi number: FoF 12449, 4 morphological species (Species Fungorum 2022), 1 species with molecular data.
Colonies fast-growing, velvety, floccose near the margin, centrally with fertile hyphal bundles with entire but vague margin. Sexual morph: Unknown. Asexual morph: Mycelium whitish, later becoming greyish brown. Submerged hyphae smooth, thin-walled. Conidiophores reduced to polyblastic conidiogenous cells arising from undifferentiated or slightly differentiated aerial hyphae, terminally integrated or lateral, rarely a branched conidiophore present, smooth, slightly thick-walled, pale brown, cylindrical to acicular, widest at the base and tapering towards the apex; apical part forming a pale brown, generally straight rachis, with crowded, prominent, blunt denticles, suggesting a gastropod radula; denticles apically pale brown. Conidia solitary, subhyaline, thin- or slightly thick-walled, smooth or verrucose, obovoidal, fusiform to subcylindrical, base sub truncate and with a slightly prominent, conspicuously pigmented hilum; conidial secession schizolytic (adapted from Arzanlou et al. 2007).
Type species: Radulidium subulatum (de Hoog) Arzanlou, W. Gams & Crous
Notes: Radulidium is characterised by whitish to greyish mycelium, polyblastic conidiogenous cells, and solitary, subhyaline, thin- or slightly thick-walled, smooth or verrucose, obovoidal, fusiform to subcylindrical conidia. Radulidium resembles Ramichloridiopsis in having conidiogenous cells with prominent conidium-bearing denticles but differs in that the latter has 2-septate, catenate, thick-walled, verrugose-striate conidia. Radulidium differs from other ramichloridium-like fungi by its somewhat differentiated conidiophores and conspicuous, blunt, very dense conidium-bearing denticles (Arzanlou et al. 2007). In the phylogenetic analysis of Arzanlou et al. (2007) based on LSU sequence data, the Radulidium clade comprised several sub clusters that relate with differences in morphology. Arzanlou et al. (2007) reported that ITS sequence data are not informative to resolve the species complex. Wu et al. (2013) added a new species R. xigazense. Wijayawardene et al. (2017, 2020) listed Radulidium in Dothideomycetes genera incertae sedis. More collections with DNA sequence data are needed to confirm the systematic position of Radulidium.