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Title: Pinus ponderosa: a taxonomic review with five subspecies in the United States
Author: Callaham, Robert Z.
Source: Res. Pap. PSW-RP-264. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 52 p
Publication Series: Research Paper (RP)
Various forms of Pinus ponderosa Douglas ex C. Lawson are found from British Columbia southward and eastward through 16 states and, perhaps, into Mexico. The status of many names previously associated with this species, but excluded here, has been clarified. Accumulated evidence based on variation in morphology and xylem monoterpenes, partial genetic barriers to crossing, and allozyme differences leads to recognition of five subspecies:
- Pinus ponderosa subsp. ponderosa, Columbia ponderosa pine, southward from southern British Columbia, east of the Cascade Range in Washington, Oregon, and northeastern California and eastward to the Continental Divide.
- Pinus ponderosa subsp. critchfieldiana Callaham, subsp. nov., Pacific ponderosa pine, from Puget Sound, Washington, southward to southern California.
- Pinus ponderosa subsp. scopulorum (Engelm. in S. Watson) E. Murray, Rocky Mountains ponderosa pine, from the Continental Divide in Montana eastward to the Black Hills of South Dakota and southward into Utah and Colorado.
- Pinus ponderosa subsp. readiana Callaham, subsp. nov., central high plains ponderosa pine, restricted to Nebraska and adjacent areas in South Dakota, Wyoming, and Colorado.
- Pinus ponderosa subsp. brachyptera (Engelm. in Wislizenus) Callaham, comb. nov., southwestern ponderosa pine, in Arizona, New Mexico, Oklahoma, and southwestern Texas, and, probably, extending into Mexico.
Transition zones occur between subspecies.
Keywords: Ponderosa pine, Pinus ponderosa, taxonomy, subspecies
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Callaham, Robert Z. 2013. Pinus ponderosa: a taxonomic review with five subspecies in the United States. Res. Pap. PSW-RP-264. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 52 p.
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