Originally, the Trichophyton (T.) mentagrophytes complex distinguished between the anthropophilic subspecies T. mentagrophytes var. interdigitale, T. mentagrophytes var. nodulare (synonym T. krajdenii), and T. mentagrophytes var. goetzii and the zoophilic subspecies T. mentagrophytes var. granulosum (rodents), T. mentagrophytes var. erinacei (hedgehog), and T. mentagrophytes var. quinckeanum (mice). In addition, two sexual species (teleomorph) of this complex are known. These are Arthroderma (A.) benhamiae Ajello and Cheng 1967 and Arthroderma vanbreuseghemii Takashio 1973.
According to recent molecular studies,the species T.mentagrophytes is synonymous with only the zoophilic subspecies T.mentagrophytes var. quinckeanum which is rare in Western Europe. The anthropophilic subspecies of T. mentagrophytes, as well as many of the zoophilic strains, formerly differentiated as var. mentagrophytes or var. granulosum, are indistinguishable and are now designated T.interdigitale.
The morphological differentiation between anthropophilic and zoophilic T. interdigitale strains by classical microscopical and biochemical methods is often problematic. In particular, it is impossible to differentiate between the zoophilic strains of T. interdigitale, T. mentagrophytes, and the Trichophyton anamorph of A. benhamiae. In these cases, molecular identification methods may be applied to answer epidemiological, taxonomical and therapeutic questions.