Phenotypic divergence between wild and cultivated plants can be difficult to achieve in sympatry due to gene flow potentially offsetting the effects of artificial selection. Despite the relevance of this topic to understanding the early stages of the domestication process, little empirical research on the subject exists. Chaya (Cnidoscolus aconitifolius), a leafy vegetable domesticated by the Peninsular Maya, is often cultivated in homegardens where wild plants of the same species may co-occur. Here, the state of the art regarding the domestication process of chaya is summarized, and our findings regarding reproductive isolation and phenotypic divergence between wild and cultivated chaya are described. According to the results, despite coexistence, a clear phenotypic divergence existed between wild and cultivated chaya, particularly in leaf and stem traits. There is significant reproductive isolation between wild and cultivated chaya. Male flowers of cultivated plants often produced little or no pollen, which contributed to reproductive isolation in the direction from cultivated to wild plants. Cultivated chaya is clonally propagated, which may have contributed to its low fertility and the characteristic phenotype seen in cultivated plants via vegetative vs sexual allocation trade-offs. In conclusion, reproductive isolation between wild and cultivated chaya is complete and evolved in sympatry.