Nassar J. M., Hamrick J. L., Fleming T. H., Allozyme Diversity and Genetic Structure of the Leafy Cactus (Pereskia guamacho [Cactaceae]), Journal of Heredity, 2002, 93(3):193-200, doi: 10.1093/jhered/93.3.193
The allozyme analysis compares seventeen Leuenbergeria guamacho populations (Pereskia guamacho in the paper) in Venezuela. It presents genetic variation within and between populations and inferences about gene exchange.