This species is similar to M.chionea, but they differ in the length of the neck [150–200(–266) μm in M.washingtonensis vs. 250–400 μm in M.chionea] and in the size of the ascospores [10.5–12(–13.5) × 9–10.5(–12) × 7–9 μm in M.washingtonensis vs. 7.5–16 × 6–12 × 4–7 μm in M.chionea], as well as in the presence of a phialidic asexual morph in M.washingtonensis.