We present a model for the gradual evolution towards dioecy in cosexual plants with geitonogamous selfing. We show how geitonogamous selfing (i.e. transfer of pollen between flowers on the same plant) can facilitate the evolution of dioecy (i.e. separate male and female individuals) in cosexual plants (i.e. both sexual functions on the same plant). We study the effect of parameters such as inbreeding depression, the attraction costs per flower, and the total amount of resources available per plant. We also consider different flower architectures (limited versus unlimited potential number of seeds per flower) and pollination biologies (biotic versus abiotic). We find that (1) if there is no maximum to the number of seeds per flower, then cosexuality is evolutionarily stable whenever the inbreeding depression is less than one-half. With abiotic pollination and an inbreeding depression greater than one-half, dioecy evolves via evolutionary branching, that is, through the gradual differentiation towards male ...