Leaf Essential Oils of the New Conifer Genus, Xanthocyparis: Xanthocyparis vietnamensis and X. nootkatensis, The

Journal of Essential Oil Research: JEOR, Jan/Feb 2007 by Adams, Robert P, Thomas, Philip, Rushforth, Keith

Abstract

A new conifer genus was recently discovered in northern Vietnam and named Xanthocyparis with two species: X. vietnamensis in Vietnam and X. nootkatensis (= Chamaecyparis nootkatensis) in western North America. This is the first analysis of the leaf essential oil of X. vietnamensis. The oil of X. vietnamensis is dominated by sesquiterpenes and diterpenes. The major components are hedycaryol (1.4-34.4%), phyllocladene (0.9-37.8%), sandaracopimara-8(14),15-diene (0.7-8.9%), germacrene D (3.7-7.9%), and α-pinene (0.8-14.9%). The oil of Xanthocyparis nootkatensis (Chamaecyparis nootkatensis) is dominated by monoterpenes. The major constituents of X. nootkatensis are limonene (35.4-42.4%), δ-3-carene (11.5-23.4%), α-pinene (8.7-16.3%) and nezukol (3.3-4.8%). The oils differ in many components but share many of the unusual diterpenes. This seems to indicate a rather distant relationship and a long period of divergence. The oil samples of X. vietnamensis were extremely variable (e.g. hedycaryol 1.4-34.4%; phyllocladene 0.9-37.8%) suggesting chemical races or botanical varieties may be present.

Key Word Index

Xanthocyparis vietnamensis, Xanthocyparis nootkatensis, Chamaecyparis nootkatensis, essential oil composition, hedycaryol, phyllocladene, α-pinene, δ-3-carene, limonene.

Introduction

In 2002, a new conifer genus, Xanthocyparis, was described from northern Vietnam. The new Vietnamese species, Xanthocyparis vietnamensis Farjon et Hiep, is restricted to a small area of karst limestone in the northern part of Hagiang Province (1). The morphological features of this new conifer strongly suggested affinity to Chamaecyparis nootkatensis (D. Don) Spach in the Cupressaceae, leading Farjon et al. (1) to move Chamaecyparis nootkatensis (D. Don) Spach to the new genus as Xanthocyparis nootkatensis ( D. Don) Farjon & Harder. Chamaecyparis nootkatensis has had a troubled taxonomic history having been placed in four different genera: Cupressus, Chamaecyparis, Callitropsis and Xanthocyparis (see Little et al. (2) for a review of the taxonomic history).

Recently, Little et al. (2), using ITS (nrDNA), matK and rbcL sequence data showed that Xanthocyparis is a distinct clade (Figure 1, 93% bootstrap) but the Xanthocyparis clade is closely related to the clade of Cupressus species from the western hemisphere (Figure 1, 92% bootstrap). Notice that a larger clade exists that contains Cupresstts from both the eastern hemisphere (EH) and western hemisphere (WH), along with Juniperus and Xanthocyparis nested between the Cupresstts (EH, WH) clades. Due to nomenclatural priority, Little et al. (2) resurrected the genus Callitropsis with two species: CaIlitropsis nootkatensis (D. Don) Orest. and C. vietnamensts (Farjon et Hiep) O.P. Little.

There are no analyses of the leaf oil of Xanthocyparis vietnamensts. The most recent complete analysis of the leaf oil of Ch. nootkatensis was by Cheng and von Rudloff in 1970 (3). Subsequently, totarol (trans-) was isolated from Ch. nootkatensis (4). Cool (5) found new ent-daucane and acoranes from x Cupressocyparis leylandii, but the compounds were not found in either of the putative parents (Ch. nootkatensis, Cup. macrocarpa).

In this work, we make the first report on the composition of the leaf oil of X. vietnamensis and compare it with detailed analyses of X. nootkatensis (Ch. nootkatensis) leaf oils.

Experimental

For X. nootkatensis (Ch. nootkatensis), leaf material was obtained by field sampling. Materials from X. vtetnamensiswere obtained from plants growing at the Royal Botanical Garden Edinburgh from young trees with mature foliage from known trees in Vietnam. Xanthocyparis nootkatensis: Adams 9086, Seattle, WA, USA, Adams 9274, 9276, Vancouver Island, BC, Canada; X. vietnamensis, To Quang Thao 16, 22, 26 at 1230 m, Hang Tong Trong mountain, Vietnam (cloned and cultivated at Royal Bot. Gard. Edinburgh as accessions 20030528, 20030532 and 20030536, respectively). Voucher specimens for Adams collections have been deposited at Baylor University Herbarium (BAYLU) and Thao collections at Royal Bot. Gard. Edinburgh (E).

Fresh leaves (200 g fresh wt) were steam distilled for 2 h using a circulatory Clevenger-type apparatus (6). The oil samples were concentrated (ether trap removed) with nitrogen and the samples stored at -20°C until analyzed. The extracted leaves were oven dried (48 h, 100°C) for determination of oil yields.

The essential oils were analyzed on a HP5971 MSD mass spectrometer, directly coupled to a HP 5890 gas chromatograph, using a J & W DB-5,0.26 mm x 30 m, 0.25 µm coating thickness, fused silica capillary column (see 7 for operating details). Identifications were made by library searches of our volatile oil library (7), using the HP Chemstation library search routines, coupled with retention time data of authentic reference compounds. Quantitation was by FID on an HP 5890 gas chromatograph using the HP Chemstation software.

Results and Discussion

The oils of the two species were very different (Table I). The oil of X. vietnamensis was dominated by sesquiterpenes and diterpenes such as hedycaryol (1.4-34.4%), phyllocladene (0.9-37.8%), sandaracopimara-8(14),15-diene (0.7-8.9%), germacrene D (3.7-7.9%). The monoterpenes were low in the common components normally found in conifers, except for cc-pinene (0.8-14.9%), which was very variable. In contrast, the oil of X. nootkatensis (Ch. nootkatensis) is dominated by monoterpenes. The major constituents of X. nootkatensis are limonene (35.4-42.4%), δ-3-carene (11.5-23.4%), α-pinene (8.7-16.3%) and nezukol (3.3-4.8%). The oils differed in many components (Table I) and this seems to indicate a rather distant relationship and a long period of divergence. This distant relationship is depicted in their DNA sequence data ( Figure 1). Notice that X. vietnamensis and X. nootkatensis form a clade supported at the 93% level, but they are closely associated with Cupressus from the western hemisphere.