Possible natural interspecific hybridization among taxa of Opuntia subgenus Opuntia was investigated in the northern Chihuahuan Desert region. The investigation employed experimental hybridization and random amplified polymorphic DNA (RAPD) data. Plants in the Sul Ross State University Garden representing three ploidy levels, ten species, and three varieties were used for all experiments. Reciprocal crosses were made between putative parental taxa, and each cross was analyzed for fruit and seed set. For each taxon, tests were performed to control for possible apomictic, autogamous, and geitonogamous seed set. Data gathered from the tests provided basic information regarding the breeding systems of the taxa investigated. Reciprocal crosses between ploidy levels set fruit and seed unidirectionally. Seed set data suggest that O. engelmannii possibly spreads primarily through vegetative means, or by dispersal of self-fertilized seed. RAPD banding pattern data suggested that at least one Opuntia population was of hybrid origin.

Key words: Chihuahuan Desert Region, hybridization, Opuntia