Butterworth C. A., Wallace R. S., Molecular Phylogenetics of the Leafy Cactus Genus Pereskia (Cactaceae), Systematic Botany, 2005, 30(4):800-808, doi: 10.1600/036364405775097806
Plastid DNA analyses reveal distinct lineages within historical Pereskia. The authors compare relationships of yellow-flowered species, among others.