The Geography of Phytochemical Races

3.1 North America 137
3.1.5 Thuja plicata-Western Red Cedar (Cupressaceae)
Thuja plicata D. Don is one of the most important forest trees in coastal, western
North America, providing a weather-resistant wood much in demand as a source of
shingles as well as for more decorative purposes. The species also has great signifi -
cance within the First Nations people throughout its range, which includes moist to
swampy sites from southern Alaska southward along the coast to Humboldt County,
California, and in central British Columbia southward through Washington, eastern
Oregon to northern Idaho and northwestern Montana. The coastal and inland ranges
of western red cedar are separated by a system of valleys that experience much
lower rainfall and thus provide few suitable habitats. Both segments of the species’
range likely represent northward advances from refugia following glacial retreat.
Patterns of variation have been studied using protein electrophoresis as well as gas
chromatographic analysis of volatile oil components. We will look at the terpene
chemistry of the species fi rst.
Interest in volatile oil chemistry of western red cedar goes back to the early days of
the twentieth century references, which can be found in von Rudloff’s (1962) paper
on gas–liquid chromatography (GLC) of red cedar terpenes. That work, although
mainly concerned with within-tree variation, did report similar analytical data from
trees sampled at some distance from each other, central versus southwestern British
Columbia. The major components of the oil were thujone [273] (76–87%), isothujone
[274] (7.0–9.0%), and sabinene [275] (1.0–8.0%) (see Fig. 3.5). Also observed,
but at much lower concentrations, were α-pinene, camphene, car-4-ene, limonene,
1,8-cineole, terpinene, p-cymene, and terpinolene. A subsequent study of terpene
variation as a function of geographic origin of the species involved material analyzed
from 29 sites in British Columbia, Idaho, Montana, Oregon, and Washington
(von Rudloff and Lapp, 1979). Analysis of quantitative values for 18 compounds
was performed using simple linkage clustering of F-1 weighted similarities.
Fig. 3.5 Compounds
273–275, terpenes from
Thuja plicata. Compounds
276 and 277, sesquiterpenes
from Ambrosia psilostachya