Isariopsis Fresen., Beitr. Mykol. 3: 87 (1863).
Index Fungorum number: IF 8639; Facesoffungi number: FoF 08619, 6 morphological species (Species Fungorum 2021), molecular data unavailable.
Phytoparasitic, mostly causing leaf spots; mycelium internal, colourless or faintly coloured, often forming stromata in the substomatal cavities, colourless to faintly coloured; conidiophores macronematous, synnematous, individual conidiophores simple, rarely branched, continuous to septate, hyaline or almost so, apically and partly laterally splaying out; synnemata at first hyaline, later colored, at least in the lower part, yellowish, yellowish-brown, brown, reddish-brown, flesh-colored; free ends of the conidiophores hyaline; conidiogenous cells integrated, terminal, polyblastic, sympodial, cicatrized, scars conspicuous, small, somewhat thickened, refractive; conidia formed singly or catenate, sometimes in branched chains, 0–1-septate, hyaline, smooth to verruculose, shape variable, ellipsoid–ovoid, fusiform, subcylindric, subglobose, irregular, hilum conspicuous, often slightly thickened, refractive (Adapted from Braun 1998).
Type species: Isariopsis pusilla Fresen.
Notes: Isariopsis was introduced by Fresenius (1863) with I. pusilla as type species. Isariopsis is currently considered as a synonym of Phacellium. Isariopsis accommodates synnematous Ramularia like taxa. Isariopsis is characterized by synnematous conidiophores, synnemata initially hyaline, becoming coloured in the lower half, free ends of the individual conidiophores hyaline, cicatrized; conidia produced singly or in chains, 0–1-septate, hyaline, typically verruculose. Isariopsis is presently considered a synonym of Phacellium but sequence data is needed to confirm the hypothesis. Braun (1988b) revised the concepts and redefined this genus. Braun (1990) debated over the nomenclature of Phacellium and Isariopsis and reintroduced the older, valid name Phacellium. Several authors suggested to reduce Isariopsis to synonymy with Ramularia (Gunnerbeck 1967; Gjaerum 1968), but the latter genus can be evidently differentiated from Isariopsis (= Phacellium) by fasciculate, free conidiophores, separated from base to apex. Conidiophores are neither tightly ad pressed nor fused. Isariopsis is currently treated as a doubtful genus in Mycosphaerellaceae.