Morphological and foliar terpene characters to distinguish between western and eastern white pine

To distinguish between western (Pinus monticola) and eastern (P. strobus) white pines, foliage, buds, and cones were examined and foliar terpenes were extracted and analyzed from representative samples. Needles of P. monticola were heavier, wider (>0.7 mm), and stiffer; buds were larger and usually nonresinous; cone scales, when viewed from the cone bottom, were arranged in five and eight spiralling rows. Needles of P. strobus were lighter, narrower (<0.7 mm), and droopy; buds were small and covered with white resin and bloom; cone scales were arranged in three and five rows. Needles and cones of P. monticola tended to be longer; cones were composed of more scales and contained more scales per centimetre and more scales per spiral row than those of P. strobus, but there was some overlap. Twig pubescence, bud apex shape, phyllotaxy, and seed wing length were not distinctive. Capillary gas-liquid chromatographic analysis of the leaf oils of white pine trees showed that bornyl acetate and β-elemene, present in P. monticola, were essentially absent in P. strobus, while α-humulene, present in P. strobus, was not found in P. monticola. In addition, the amount of β-caryophyllene could be used to differentiate between these species. However, the most obvious discriminating feature was the presence of a substantial and broad peak of unknown and decomposing compound(s) in the chromatograms for P. monticola and its complete absence in the chromatograms for P. strobus. A clone that was highly resistant to blister rust and previously classified as P. monticola is shown by terpene patterns and morphology to be P. strobus. Key words: Pinus monticola, Pinus strobus, terpene, Cronartium, morphology.