Abstract
Introduction
Larix occidentalis Nutt. (western larch, Pinaceae) is found naturally in the mountains of southwestern Canada (Alberta and British Columbia) and northwestern United States (Idaho, Montana, Oregon, and Washington) (Figure 1). The tree grows up to 50 m in height; the leaves (needles) are 2-5 cm long and 0.6-0.8 mm wide; the bark is reddish brown, scaly, with deep furrows between flat, flaky, cinnamon-colored plates; the seed cones are 2-3 cm × 1.3-1.6 cm (Figure 2). 1

Range of Larix occidentalis Nutt. 2

Larix occidentalis Nutt.
Several Native American tribes used L. occidentalis as part of their traditional herbal medicine. 3 The Nez Perce Native Americans used infusions of the bark of L. occidentalis to treat coughs and colds. 3 The Okanagan-Colville people used a decoction of the plant (both externally and internally) treat arthritis and externally to wash cuts and sores. 3 The Thompson people used a decoction of the branches to treat coughs. 3 Similarly, Larix decidua (L.) Mill. has been used in traditional herbal medicine in Europe to treat the common cold,4,5 coughs, 6 wounds,7,8 and sore joints. 9
Essential oils are complex mixtures of volatile, hydrophobic compounds that are typically obtained by hydrodistillation or steam distillation of plant materials, but may also be obtained by cold pressing or enfleurage. 10 The compositions of essential oils are very complex and may contain more than 200 individual components. The compound classes making up essential oils are typically monoterpenoids, sesquiterpenoids, diterpenoids, fatty acid derivatives, and phenylpropanoids.11,12 Essential oils have shown various biological activities including antibacterial, antifungal, 13 allelopathic, 14 and pesticidal. 15 Due to these attributes, essential oils have demonstrated valuable applications in various fields including agriculture, 16 the food industry,17,18 the flavor and fragrance industry, 19 cosmetics, 20 aromatherapy, 21 and drug discovery. 22 As part of our ongoing interest in aromatic and medicinal plants as well as gymnosperm essential oils, this report presents the essential oil composition and the enantiomeric distribution of chiral monoterpenoids of L. occidentalis growing in Idaho. This present work complements previous older examinations of L. occidentalis23,24 and includes enantioselective gas chromatographic evaluation, which broadens our understanding of the volatile composition of this species.
Materials and Methods
Plant Material
Foliage of L. occidentialis was collected from three individual trees located on Brundage Mountain, Idaho, on 31 May 2024. Twigs from several sites on the tree were obtained and pooled for each individual tree. The trees were identified in the field by W.N. Setzer and confirmed by comparison with samples from the C.V. Starr Virtual Herbarium. 25 A voucher specimen (WNS-Locc-5826) was deposited with the University of Alabama in Huntsville herbarium. The plant material was stored frozen (–20 °C) until processing. The foliage was hydrodistilled for 4 h using a Likens-Nickerson apparatus as previously described 26 to give yellow essential oils (Table 1).
Collection and Hydrodistillation Details for Larix occidentalis Individual Trees.
Gas Chromatographic Analyses
The L. occidentalis foliar essential oils were subjected to gas chromatographic analyses (GC-FID, GC-MS, and enantioselective GC-MS) as previously described. 26 The chromatographic details are provided as Supplemental material (Supplemental Table S1).
Hierarchical Cluster Analysis
Hierarchical cluster analysis (HCA) was carried out using XLSTAT v. 2018.1.1.62926 (Addinsoft, Paris, France). The percentages of the fifteen most abundant components (α-pinene, camphene, sabinene, β-pinene, myrcene, δ-3-carene, limonene, β-phellandrene, 1,8-cineole, β-ocimene, terpinolene, α-terpineol, bornyl acetate, germacrene D, and (E)-nerolidol) from this study and the compositions from other Larix species previously reported23,24,27-32 were used for the analysis. Dissimilarity was used to determine clusters considering Euclidean distance and Ward's method was used to define agglomeration.
Results
Essential Oil Composition
Foliage (terminal twigs and leaves) from three individual trees growing on Brundage Mountain, Idaho, were collected. Hydrodistillation of the foliage of L. occidentalis gave yellow essential oils in yields of 1.253-1.773% (Table 1). Gas chromatographic analysis of the essential oils allowed for identification of a total of 117 chemical components collected from three individual trees, which accounted for 98.2-99.6% of the total essential oil compositions (Table 2, Supplemental Figure S1). Monoterpene hydrocarbons (55.0-65.9%) and oxygenated monoterpenoids (17.0-24.1%) dominated the foliar essential oils of L. occidentalis. Sesquiterpene hydrocarbons (4.1-10.3%), oxygenated sesquiterpenoids (3.4-6.1%), and diterpenoids (2.3-3.6%) were minor constituents. The major components in the essential oils were α-pinene (26.5 ± 5.4%), β-pinene (14.9 ± 2.5%), α-terpineol (8.3 ± 1.2%), and δ-3-carene (6.6 ± 2.9%).
Chemical Composition (Percentage) of the Foliar Essential Oil of Larix occidentalis.
Enantiomeric Distribution
The L. occidentalis essential oils were subjected to enantioselective GC-MS. The enantiomeric distributions of the monoterpenoid components are listed in Table 3. The enantiomeric distributions for α-pinene and verbenone were variable (virtually racemic). Sabinene was also variable, but (–)-sabinene was dominant in two of the three samples. The (–)-enantiomers were slightly dominant for limonene (58.8 ± 1.2%) and terpinen-4-ol (58.5 ± 1.4%), and (–)-enantiomers were dominant for camphene (84.1 ± 6.6%), β-pinene (97.7 ± 0.4%), β-phellandrene (80.6 ± 3.2%), borneol (86.2 ± 0.9%), and α-terpineol (85.4 ± 4.6%). (+)-δ-3-Carene was the only enantiomer observed.
Enantiomeric Distributions (Percent) of Monoterpenoid Components in Larix occidentalis.
RIcalc = Calculated retention index determined with respect to a homologous series of n-alkanes on a B-Dex 325 chiral capillary column. RIdb = Retention index values obtained from our own database using available reference compounds. n.d. = compound not detected. n.a. = reference compound not available.
Discussion
Essential Oil Composition
This is the first report on the essential oil of L. occidentalis from Idaho, USA. Interestingly, the sesquiterpene hydrocarbon concentration was lower in tree C (4.1%) than those in trees A and B (9.6% and 10.3%), which is attributed to the lower concentrations of (E)-β-caryophyllene, germacrene D, and δ-cadinene in tree C. It is not clear why the sesquiterpenes were lower in tree C; the samples were collected from similar locations on the same day. There have been older reports on L. occidentalis from Canada 23 and chloroform extracts from Montana. 24 In addition, there have been several reports on other Larix species, namely L. decidua,27-30 Larix kaempferi (Lamb.) Carrière, 31 Larix laricina (Du Roi) K.Koch, 23 Larix leptolepis (Siebold & Zucc.) Gordon (syn. Larix kaempferi (Lamb.) Carrière), 29 and Larix sibirica Ledeb.29,32 The major essential oil components of the previously published Larix essential oils are summarized in Table 4. In order to visually compare the essential oil compositions, a hierarchical cluster analysis (HCA) was carried out using the major components (Figure 3). The dendrogram from the HCA can be divided into four clusters: (1) an α-pinene/β-pinene group, (2) a sabinene/α-pinene group (one sample), a group dominated by α-pinene, and a δ-3-carene/α-pinene group. The HCA clearly shows that the three L. occidentalis essential oil samples from Idaho are very similar to each other as well as to the L. occidentalis sample from British Columbia, and fall into the α-pinene/β-pinene group. The major components observed in L. occidentalis are consistent with those found in other Larix essential oils. That is, α-pinene and β-pinene are major components in Larix essential oils.

Dendrogram Obtained by Hierarchical Cluster Analysis (HCA) of Major Volatile Components of Larix Species. L. occidentalis (Idaho) this Work, L. occidentalis (British Columbia), 23 L. lyallii (Alberta), 23 L. leptolepis (Finland), 29 L. decidua (Finland), 29 L. kaempferi (Korea), 31 L. laricina (Yukon), 23 L. occidentalis (Montana), 24 L. decidua (Corsica), 27 L. lyallii (Montana), 24 L. decidua (Italy), 28 L. decidua (Italy, commercial), 30 L. sibirica (Finland), 29 L. sibirica (Siberia). 32
Major Essential Oil Components from Larix Species.
aReported as D-limonene, but an enantioselective GC column was not used.
b(E)/(Z)-Isomer not indicated. Based on the retention index, this may be β-phellandrene.
cIndividual enantiomers of α-pinene, β-pinene, limonene, and bornyl acetate were indicated, but an enantioselective GC column was not used.
dThis was a chloroform extract and not an essential oil.
eLabeled as β-cubebene, but more likely this is germacrene D.
The biological activities of the major L. occidentalis essential oil components, α-pinene,38,39 β-pinene, 38 and α-terpineol40,41 have been reviewed. α-Pinene has shown antibacterial, antifungal, anti-inflammatory, analgesic,38,39 and wound-healing 42 activities. β-Pinene has shown antimicrobial activity 38 ; and α-terpineol has shown anti-nociceptive, anti-bronchitis, antimicrobial, and anti-inflammatory effects.40,41 Thus, the biological activities of the major components are consistent with the traditional uses of L. occidentalis to treat coughs, arthritis, and cuts and sores.
Enantiomeric Distribution
Holm and Hiltunen have carried out enantioselective GC-MS analysis of L. decidua, L. leptolepis, and L. sibirica leaf essential oils. 29 In that study, the enantiomeric distribution in α-pinene was variable, but the (–)-enantiomers were dominant for camphene, β-pinene, limonene, and β-phellandrene, while the (+)-enantiomers dominated in sabinene and δ-3-carene. Thus, the enantiomeric distributions of monoterpenoids in Larix species are relatively consistent.
Conclusions
This work reports, for the first time, the essential oil composition of Larix occidentalis collected from Brundage Mountain, Idaho. The essential oils were dominated by monoterpenoids, including α-pinene (26.5 ± 5.4%), β-pinene (14.9 ± 2.5%), α-terpineol (8.3 ± 1.2%), and δ-3-carene (6.6 ± 2.9%). The limitation of this current work is that only three samples of foliage were collected from one general area (Brundage Mountain, Idaho). Furthermore, previous investigations of Larix essential oils are either old, incomplete, or sparse. Additional work is needed to more clearly define the essential oil compositions of these species, including essential oils from the leaves and from the bark. In addition, more modern biological screening of the essential oils, their major components, and mixtures of components would help to corroborate the traditional uses of Larix species.
Supplemental Material
sj-docx-1-npx-10.1177_1934578X251334214 - Supplemental material for Chemical Composition and Enantiomeric Distribution of the Essential oil of Larix occidentalis Nutt
Supplemental material, sj-docx-1-npx-10.1177_1934578X251334214 for Chemical Composition and Enantiomeric Distribution of the Essential oil of Larix occidentalis Nutt by Ambika Poudel, Prabodh Satyal, Kathy Swor and William N Setzer in Natural Product Communications
Supplemental Material
sj-docx-2-npx-10.1177_1934578X251334214 - Supplemental material for Chemical Composition and Enantiomeric Distribution of the Essential oil of Larix occidentalis Nutt
Supplemental material, sj-docx-2-npx-10.1177_1934578X251334214 for Chemical Composition and Enantiomeric Distribution of the Essential oil of Larix occidentalis Nutt by Ambika Poudel, Prabodh Satyal, Kathy Swor and William N Setzer in Natural Product Communications
Footnotes
Acknowledgments
Statement of Human and Animal Rights
This article does not contain any studies with human or animal subjects.
Ethical Considerations
Ethical approval is not applicable for this article.
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Funding
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Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Data Availability
All the data for this study are available in the manuscript.
Supplemental Material
Supplemental material for this article is available online.
References
Supplementary Material
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