We describe a new species of leptodactylid frog of the genus Physalaemus from the lowlands of western Ecuador. It belongs to the P. pustulosus species group and differs from other group members in its smaller size, skin texture, tadpole characters, and advertisement call. The new species has wide variation in size and color pattern both at the intra- and inter-population levels. This variation matches that observed in P. montubio and P. randi, and render difficult its diagnosis on the basis of morphological features. A phylogenetic analysis of morphological characters shows that the new species belongs to a clade distributed west of the Andes in Ecuador and northern Peru, sister to (P. petersi P. pustulosus). A phylogeny based on mtDNA shows that P. montubio and P. randi form a clade sister to (P. coloradorum P. sp. nov.). The calls of these three species have two components with different acoustic features that arguably match the frequency sensitivity of the ear of conspecific females, in a manner similar to the complex calls of P. pustulosus. The new species occurs in two predominantly dry regions, the Lowland Deciduous Costa Forest, and the Lowland Semideciduous Costa Forest.