Four new species of "non-spiny" Solanum from South America are described. Solanum longifilamentum Särkinen & P.Gonzáles, sp. nov. (Morelloid clade) is widespread from Ecuador to Bolivia and is most similar to S. macrotonum Dunal from Central and northern South America. Solanum antisuyo Särkinen & S.Knapp, sp. nov. (Morelloid clade) is found on the eastern Andean slopes in Ecuador, Peru and Bolivia and is most similar to the widespread lower elevation species S. polytrichostylum Bitter. Solanum arenicola Särkinen & P.Gonzáles, sp. nov. (Morelloid clade) is found in low elevation habitats on the eastern Andean slopes and in Amazonia of Peru and Bolivia and is most similar to the higher elevation species S. aloysiifolium Dunal of Bolivia and Argentina. Solanum mariae Särkinen & S.Knapp, sp. nov. (Potato clade) is endemic to Cajamarca Department in Peru, and is most similar to the widespread S. caripense Dunal. Complete descriptions, distributions and preliminary conservation assessments of all new species are given.