Terpenoid chemosystematic studies of Abies grandis

Cortial essential oil from 395 typical Abies grandis and Abies grandis-Abies concolor intermediate trees collected in 48 locations was analyzed for composition of its monoterpenoids. The monoterpenoids were composed primarily of α-pinene, camphene, β-pinene, β-phellandrene and bornyl acetate, with tricyclene, 3-carene, myrcene and limonene in secondary quantities. Camphene, present in larger amounts in A. grandis and in smaller amounts in A. concolor var. lowiana, was used as a marker for studying intergradation of the two species in western and northwestern United States. A. grandis from northern Montana, Idaho and Washington, from British Columbia and Oregon and from Washington coastal areas could be classified as typical while the rest of the populations showed various degrees of intermediacy. The variability patterns agreed with the hypothesis that introgressive hybridization was the main reason for the intermediacy. Compared with morphological evaluations, the intermediate populations were chemically significantly more A. concolor-like. Typical A. grandis exhibited little population-to-population variability, in spite of its large geographic range. The results are correlated with and explained on the basis of existing paleobotanical records.