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).
- Burns, Russell M., and Barbara H. Honkala, technical coordinators. 1990. Silvics of North America: 1. Conifers; 2. Hardwoods. Agriculture Handbook 654 (Supersedes Agriculture Handbook 271,Silvics of Forest Trees of the United States, 1965). U.S. Department of Agriculture, Forest Service, Washington, DC. vol.2, 877 pp. http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm
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