The leaf essential oils of the genus Calocedrus

Farjon (1) considers the genus Calocedrus as containing just three species, C. decurrens (w. N. America), C. macrolepis (S.W. China, N. Vietnam, N. Thailand) and C. formosana (Taiwan). The leaf oils were analyzed and compared to the oil of the closely related species, Platycladus orientalis (E., N.E. China, Korea, far eastern Russia). The oils of C. macrolepis and C. formosana were very similar, being high in alpha-pinene (57.2% and 67.1%, respectively) and myrcene (11.2% and 6.2%), but they differed in several smaller components. The oils of C. decurrens from two populations in Oregon and one disjunct population in southern California were high in delta-3-carene (15.2-20.2%), limonene (18.2-23.6%), alpha-pinene (8.7-15.8%), terpinolene (5.7-8.0%), alpha-fenchyl acetate (3.5-9.7%), with some cedrol (0.8-1.2%). No large differences in oil compositions were seen between the three C. decurrens populations. Platycladus orientalis (= Thuja orientalis, = Biota orientalis) was found to contain considerable amounts of delta-3-carene (29.8%), cedrol (22.2%), alpha-pinene (15.1%) and terpinolene (4.9%). Overall, the oil of C. decurrens is as different from C. macrolepis and C. formosana as it is from P. orientalis, suggesting considerable divergence between Calocedrus species, but not between C. macrolepis and C. formosana. These leaf oil analyses support the recognition of C. macrolepis var. formosana in Taiwan as treated in the Flora of China.