The Geography of Phytochemical Races

3.2 North American Conifers 147
camphor, which occurs in higher concentrations in western trees, and bornyl acetate,
which is present in larger amounts in eastern trees. This geographic differentiation
parallels the fi ndings of Wilkinson et al. (1971) who studied oleoresin composition
in representatives of 16 populations maintained in a common plantation in southern
Michigan. Two clusters emerged from their study, one that encompassed trees from
the Great Lakes northeast to Labrador, and one that extended northwestward to
Alaska. Trees from the eastern type had signifi cantly higher amounts of β-pinene,
3-carene, and β-phellandrene, whereas limonene was present in higher concentrations
in western trees.
In von Rudloff’s leaf oil study, distinctly different profi les appeared in certain
valleys in the Rocky Mountains and in central British Columbia where the ranges
of white spruce and Engelmann’s spruce overlap. Hybridization with subsequent
introgression has resulted in individuals with greater or lesser amounts of marker
compounds indicating several degrees of backcrossing. von Rudloff’s review is
extensive and should be consulted for additional examples and greater detail.
3.2.4 Pinus (Pinaceae)
Pinus is well represented in the North American fl ora with several species having
been thoroughly studied with respect to terpenoid composition. A few selected
examples will demonstrate the usefulness of these compounds in studying relationships
and migrational history of members of this moderately large genus. Examples
to be discussed range from commercially important species such as P. contorta,
(lodgepole pine), P. monticola (western white pine), and P. ponderosa (ponderosa
pine) to the bristlecone pines, noteworthy because of their exceptional age.
3.2.4.1 Lodgepole Pine
Pinus contorta Dougl. ex Loudon, the lodgepole pine, occurs in a variety of habitats
over extensive ranges in western North America. The morphological variation,
and to some extent, its geography, led Critchfi eld (1957) to recognize four
subspecies: subsp. contorta, the coastal form that extends from Alaska to northern
California; subsp. bolanderi (Parl.) Critchf., which occurs in an isolated pocket
north of San Francisco; subsp. murrayana (Grev. and Balf.) Critchf., which
occurs in the Cascades Range and south through the Sierra Nevada and into the
San Bernardino Mountains; and subsp. latifolia Engelmann, which occurs from
the interior of British Columbia, north to the Yukon, and east to Alberta and the
Rocky Mountains. Earlier studies of terpenes of lodgepole pine, reviewed briefl y
by Forrest (1980a), were suffi cient to reveal signifi cant variation, but not comprehensive
enough to allow any clear-cut chemical types to be defi ned. A study
of geographic variation of lodgepole pine in relation to population history was
published by Cywnar and MacDonald (1987).