Races and Hybrids Two distinct varieties have been recognized in the United States. Juniperus virginiana var. crebra (Fernald) is a northern form having a narrow crown and slightly pitted seeds. The other variety, J. virginiana var. ambigens, is an intermediate form between eastern redcedar and creeping juniper, J. horizontalis Moench (15).
Although there are no recognized hybrids at this time, evidence is mounting that hybridization does occur. Population studies, especially in the western part of eastern redcedar's range, suggest that considerable introgression and perhaps blending of genetic differences have occurred whenever species' ranges overlap; and that J. virginiana readily hybridizes with J. scopulorum, J. horizontalis, and J. ashei, resulting in juniper populations that contain the germ plasm of two or three species (15). Research in the Ozarks, however, showed no evidence of introgression into J. ashei by J. virginiana where J. ashei was surrounded by J. virginiana (2).
The relatively strong influence of J. scopulorum germ plasm in the western part of the eastern redcedar population suggests that the entire population in the area studied is of hybrid origin (41). This west-to-east flow of J. scopulorum germ plasm was further supported by Flake, Urbatch, and Turner (14), who sampled many of Van Haverbeke's sample trees for terpenoid analysis. He proposed an alternative hypothesis that eastern redcedar of eastern and central North America may have been derived from the western juniper complex.
- 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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