The Geography of Phytochemical Races

2.7 North and Central America 107
Fig. 2.68 Compounds
215–220, terpenes from
Satureja douglasii
position of oxygenation on the terpene ring is under genetic control (see Lincoln
and Langenheim, 1976, for leading references). The general assumption is made
that partitioning of carbon into pathways leading to monocyclic versus bicyclic terpenes
is also under genetic control. Plants transplanted to a common garden from
their respective locations along the transect remained true to their fi eld-observed
terpene type, although the relative amounts of terpenes varied somewhat; these differences
did not affect the overall pattern.
The most geographically localized terpene phenotype, referred to as the pulegone
type, occurs in the extreme southern portion of the range of the species, roughly
from the Santa Barbara area (33°29′N, 119°01′W) north to the Monterey Peninsula
(36°35′N, 121°55′W). This type consists of ca. 40% pulegone, with lesser amounts
of camphor and camphene [amounts estimated from Fig. 2.3 of the Lincoln and
Langenheim (1976) paper]. The isomenthone type overlaps the pulegone type very
slightly in the south, and extends north to the vicinity of Ukiah (Mendocino County)
(39°09′N, 123°12′W). This type consists of roughly equal amounts of isomenthone,
camphene, and camphor. The carvone type overlaps the prior two types ranging,
roughly, from the San Luis Obispo area (35°16′N, 120°40′W) to somewhat south
of Ukiah. Carvone is the prominent component in this type and occurs with camphene
and camphor. The menthone type, which consists of camphor, camphene, and
menthone—concentrations decreasing in that order—extends roughly from the San
Francisco Bay area north to near Salem, Oregon (44°57′N, 123°01′W). The most
widespread is the bicyclic type, which consists of camphor and camphene with
the former contributing the larger share. This type extends from the San Francisco
Bay area north through Oregon, Washington, and into British Columbia. By plotting
the concentrations of terpenes as a function of latitude, the investigators noted
discontinuities with both the bicyclic and p-menthane derivatives (refers to cumulative
monocyclic compounds). p-Menthane derivatives were highly correlated
with latitude from 34°N to 41°N (r = 0.−801, P < 0.01). However, concentrations of
p-menthane derivatives from more northerly sites (41–50°N) did not correlate with
latitude (r = −0.067). The total concentration of bicyclic compounds also correlated