Microtheciumbrevirostratum together with Mi.fayodii and Mi.pegleri produces ostiolate ascomata, smooth-walled, ellipsoidal to navicular or citriform ascospores and bulbils. Microtheciumbrevirostratum is easily distinguished by ascospores with apiculate germ pores and the presence of a phialidic asexual morph (ascospores show depressed germ pores and lack an asexual morph in other species). Microtheciumfayodii and Mi.pegleri differ in the size of the ascospores, Mi.pegleri having the smallest ascospores in Microthecium [(9.5–)11–12(–13) × 4–4.5 µm].