The Geography of Phytochemical Races

146 3 After the Ice
populations, representing Goose Nest Mountain in eastern Siskiyou County, were
not separated from each other and were only peripherally separated from populations
4 and 5. Separation of the populations at the northern and southern extremes
of the species would seem to offer support for the recognition of the subspecies.
Problems arise, however, in that the populations in the middle of the range do not
fall nicely into either camp. The conclusion of the authors that the terpene data
do not support recognition of infraspecifi c taxa seems reasonable. The unexpected
similarity of populations 3 and 7 from Goosenest Mountain prompted Dodd and
Rafi i (1994) to examine a larger sample for terpene variation. Fifty-one trees from
fi ve populations were analyzed and found to exhibit a larger level of chemical and
genetic variation than seen in any other population. This was in total agreement with
earlier morphometric studies. The authors suggested that these levels of variation
could be accounted for if the Goosenest Mountain area is considered as a region
of transition for the species. Further, the high level of variation between adjacent
populations was taken to indicate restricted gene fl ow within the species.
3.2.3 Picea (Pinaceae)
Picea—the spruces—consists of about 40 species (Mabberley, 1997, p. 555), members
of which occur widespread in cooler habitats in the Northern Hemisphere.
Picea is a major element in the forest fl ora of many areas of North America:
P. breweriana S. Wats. (Brewer’s spruce) of central California; P. engelmannii
Parry (Engelmann’s spruce) of western North America; P. glauca (Moench) Voss
and P. mariana (Mill.) B.S.P. (white and black spruce, respectively) of boreal North
America; P. pungens Engelm. (blue or Colorado spruce) of the Rocky Mountains;
P. rubens Sarg. (red spruce) of eastern North America; and P. sitchensis (Bong.)
Carr. (Sitka spruce) of the Pacifi c coast. All of these species have been examined
chemically to a greater or lesser extent. Much of the earlier information on chemotaxonomic
studies of spruce, along with other conifer genera, has been reviewed by
von Rudloff (1975).
The value of spruce-oil chemistry in sorting out problems of hybridization and
introgression—major factors in Picea taxonomy—was succinctly summarized by
von Rudloff who defi ned three situations: (1) Terpene variation is limited such that
it is not possible to use these characters in studies of introgression; this is the case
in eastern North America where the ranges of black spruce and red spruce overlap.
(2) Suffi cient variation in terpene profi les exists for the compounds to be useful
markers in systematic studies as seen in white spruce, Brewer’s spruce, and Sitka
spruce. (3) Tree-to-tree variation in terpene content is so variable that use in chemosystematic
studies is precluded, or at least requires very large sample sizes for
statistical reliability, as seen with Engelmann’s spruce.
The overall usefulness of terpene data for defi ning geographical races is shown
in the comparison of profi les of eastern and western white spruce (see von Rudloff,
1975, for specifi c citations). Leaf oil analysis revealed consistent differences in