Lithobium is a monotypic genus in the Melastomataceae restricted to southeastern Brazil. Most previous students of the family have placed these diminutive herbs into the Microlicieae, but some classifications have assigned the genus to the Sonerileae or Bertolonieae. Eriocnema is also a monotypic genus that has been included in the Bertolonieae, Sonerileae, and also Microlicieae. Ochthephilus, yet another monotypic genus, was assigned to the Merianieae, but lack of fruits and seeds, and a paucity of collections, have made it difficult to correctly place in a phylogenetic context. In this phylogenetic analysis, 91 species representing 73 genera from across the Melastomataceae, including 24 of the 27 genera putatively closely related to Lithobium, Eriocnema, Ochthephilus, and Physeterostemon were sampled for seven molecular markers, i.e., the nuclear ribosomal external transcribed spacer region (ETS) and internal transcribed spacer region (ITS), the plastid accD–psaI spacer region, ndhF, psbK–psbL, rbcL, and rpl16. Lithobium is on an isolated branch and is not a member of any other clade, thus a new tribe, Lithobieae, is proposed to accommodate it. In this analysis, Eriocnema and Ochthephilus form a clade including Physeterostemon that is sister to the Miconieae and separate from tribes that they have been associated with in historical classifications, thus another new tribe, Eriocnemeae, is proposed.