Gladiator Frogs (Boana) is a Neotropical group comprised of 92 species sorted into seven species groups. Herein, we present a phylogeny of the Boana semilineata species group, including all valid nominal species currently or suspected to be assigned to it— many sequenced for the first time. Parsimony and maximum likelihood analyses of two genes (16S and COI) did not support the monophyly of the B. semilineata group as currently defined. To remedy this, B. secedens, currently assigned to the B. puchella species group, is transferred to the B. semilineata group. On the other hand, our analyses corroborate the inclusion of B. hutchinsi, B. pombali and B. wavrini in the B. semilineata group. The reinterpretation of the morphology of the lower palpebral membrane in B. pombali (previously described as absent, but actually present) corroborates that the reticulated membrane is a synapomorphy of this species group (albeit homoplastic—present in a few species not assigned to this group). A recent paper suggested (based on the analyses of 16S alone) that at least six unnamed taxa (candidate species) are hidden behind the names B. geographica and B. semilineata. Our analyses resulted in the discovery of additional unnamed lineages, one of which is described and named herein. This new species is diagnosed, among other characters, by having the flanks, anterior and posterior surfaces of thigh with dark brown or blackish stripes, and by the presence of a prepollex forming a projecting spine.