Population Differences    A form of pinyon that extends southeastward from northwestern Arizona  into southwestern New Mexico in the mountains south of the Mogollon Rim  has been classified as a taxonomic variety, P. edulis var. fallax  (47). Others considered it a local variant of singleleaf pinyon (44). More  recently, however, it has been recognized as a subspecies of a newly  described species of nut pine- Pinus californiarum subsp. fallax  (Arizona single-needle pinyon) (5).

    Practically no information is available regarding population differences  of pinyon. Considering the wide range of the species and the different  environmental conditions under which it grows, differences would be  expected. It has been reported that seed size is relatively consistent  from year to year in individual trees but varies among trees (67). Also,  some trees generally produce more cones than others, and some bear larger  cones with more seeds per cone.

    Races and Hybrids    No races of pinyon have been recorded. Natural hybridization has been  reported between pinyon and singleleaf pinyon in three zones common to the  species-the eastern edge of the Great Basin, the mountains south of the  Colorado Plateau, and areas adjacent to the Colorado River and its major  drainages (44). The two species also have been artificially crossed.  Pinyon and the newly described Arizona single-needle pinyon also are known  to hybridize (5).