Four new Viola species from southern China, i.e. Viola qingruii, V. heyuanensis, V. chaozhouensis, and V. longissima, are described and illustrated based on morphology and molecular phylogeny. Viola qingruii is widely distributed in the coastal mountains of southeastern China, while V. heyuanensis, V. chaozhouensis, and V. longissima, are all narrow endemics in Guangdong Province, China. These species are described and compared with the morphologically related species V. lucens, V. tenuis, V. guangzhouensis and V. huizhouensis. Phylogenetic analysis based on ITS confirmed that all of the four new species belong to Viola sect. Plagiostigma subsect. Diffusae. An identifcation key is provided to distinguish the four new species from other species of V. subsect. Diffusae in southern China. In addition, the origin and evolution of characters such as aerial stems, stolons, elaiosomes and tuberculate seeds in Viola are briefly discussed.