The Geography of Phytochemical Races

3.2 North American Conifers 149
high concentrations of any given terpene represent a derived or an ancestral trait.
Until a gene sequence-based analysis of this system (and, it follows, the others of
this sort) we are left with no defi nitive idea of the group’s evolutionary history.
Pinus albicaulis Engelm., the whitebark pine, is a timberline species that
ranges from central British Columbia south through the Sierra Nevada Mountains
of California and from the Rocky Mountains of eastern British Columbia through
Idaho and western Montana into northwestern Wyoming, with a disjunct population
in the Ruby Mountains in Nevada (Elko County). There are several reports
of chemical constituents of whitebark pine in the literature, but the most comprehensive
examination comes from the work of Zavarin et al. (1991), who studied
the wood monoterpenes from 243 trees representing 24 populations. Four groups
were clearly delineated when the complete data set was subjected to discriminantfunction
analysis: (1) an eastern group encompassing the Rocky Mountains plus
populations sampled in eastern Oregon and northeastern Nevada; (2) a northwestern
group encompassing the coast ranges of British Columbia, Washington,
and the northern half of the Oregon Cascades; (3) a small intermediate group
consisting of populations in the southern half of the Oregon Cascades; and (4) the
Californian group. The most striking difference observed, evident even in simple
inspection of the data, was the very high levels of 3-carene in the Californian
populations. Table 3.1 presents the mean concentration values for 3-carene and
selected other monoterpenes taken from Table 3 of Zavarin et al. (1991).
The predominance of 3-carene in the Californian chemotype provides an excellent
opportunity to explore the usefulness of this compound in chemosystematic
and phytogeographical studies. Whereas concentrations of most monoterpenes seen
in the studies described here are distributed to a greater of lesser degree around
a single central value, concentrations of 3-carene frequently exhibited a trimodal
distribution. This led to the suggestion that genetic control of 3-carene biosynthesis
could be accounted for by a single locus two-allele model, with allele C coding for
high concentration of 3-carene and allele c coding for low. The heterozygous condition,
Cc, then would yield an intermediate amount of 3-carene. (Hanover, 1966a;
see also, Hanover, 1966b, 1971).
Table 3.1 Concentrations of selected monoterpenes from populations of Pinus albicaulis (from
Zavarin et al., 1991)
Terpene Location (Number of populations)
Eastern (9) Northwestern (4) Intermediate (2) Californian (9)
α-Pinene 25.1 (7.7) a 12.7 (4.6) 8.7/5.6 5.5 (2.3)
β-Pinene 10.0 (5.4) 14.8 (4.6) 6.2/5.6 1.9 (1.6)
3-Carene 20.2 (8.5) 26.6 (8.5) 53.5/52.7 70.0 (6.2)
Limonene 23.5 (7.3) 11.8 (1.8) 7.3/8.5 4.5 (1.9)
β-Phellandrene 10.8 (4.0) 15.5 (8.1) 1.6/1.4 1.5 (1.7)
Terpinene 0.6 (0.3) 2.2 (1.7) 2.2/1.2 3.0 (1.2)
p-Cymene 0.5 (0.3) 0.9 (0.7) 0.8/3.3 1.2 (0.7)
a Percentage means and standard deviations, except for intermediate populations where percentage
values only are available.