Geranium section Brasiliensia (Geraniaceae) consists of three species centered in Southern Brazil: G. arachnoideum, G. brasiliense, and G. glanduligerum. Fruits with “Erodium-type” dispersal have been found in all species of section Brasiliensia, which allows classifying this section within subg. Erodioidea. Diagnostic morphological features are analyzed and compared to other sections of Geranium subg. Erodioidea. No new characters explaining phylogenetic relationships within subg. Erodioidea or supporting its monophyly are found. A new key is provided, as well as new and detailed descriptions. Geranium brasiliense and G. glanduligerum are here illustrated for the first time. Three lectotypes are designated, and a distribution map is presented.