Species currently assigned to Rhizopogon Fr. & Nordh. can be divided into at least two groups on the basis of basidial morphology and hymenophoral development. It is desirable that two genera should be recognized but problems of typification preclude a formal proposal to this effect. One group contains species with clearly dimerous basidia which are commonly associated with swollen, thickened or gelatinized basidioles and often arise laterally from these. The other is composed of species with clavate or cylindrical non-dimerous basidia which are not associated with modified basidioles. These observations show the potential value of using the developmental anatomy of the hymenophore in the taxonomy of Gasteromycetes. Fresh specimens in various stages of development are desirable; mature or dry specimens usually prove unsatisfactory.