Individuals representing the genus Persea, subgenus Persea were assayed for restriction fragment length polymorphisms in their chloroplast genome, nuclear ribosomal DNA, and the genes coding for the enzyme cellulase. The subgenus Persea appears to consist of P. schiedeana and a separate taxon containing the remaining species. P. americana does not appear to be a monophyletic group. If P. americana is to be maintained as a species containing var. americana, var. drymifolia, and var. guatemalensis, then our data suggest that it should also contain varieties corresponding to P. floccosa, P. nubigena, and P. steyermarkii. P. americana var. guatemalensis appears to have originated as a hybrid between P. steyermarkii and P. nubigena. The root-rot-resistant cultivar G755A is a hybrid progeny of P. schiedeana and P. americana var. guatemalensis. The three varieties of P. americana were all distinguished by mutations.