1.   Introduction

There are around 250 species of Eriogonum (Polygonaceae), which are found naturally in North and Central America [1]. Of these, Eriogonum ovalifolium Nutt. (cushion buckwheat) is restricted to western North America (British Columbia and Saskatchewan, south through Washington, Idaho, Montana, Oregon, Wyoming, California, Nevada, Utah, western Colorado, and into northern Arizona and northwestern New Mexico [2]. According to Flora of North America, there are 11 varieties of Eriogonum ovalifolium [3]. Eriogonum ovalifolium var. depressum Blankinship ranges in the Rocky Mountains of Alberta, Idaho, western Montana, and Wyoming, and in desert regions of eastern Oregon [4]. The plant is characterized by greenish, elliptic or oblong to spatulate, tomentose leaves (0.4-10 cm); the scapes are generally suberect to decumbent, usually thinly floccose (Fig. 1) [3]. As part of our interest in researching the essential oils of aromatic and medicinal plants of the intermountain western United States, we present the essential oil obtained from aerial parts of E. ovalifolium var. depressum collected from southeastern Oregon. To the best of our knowledge, there have been no previous reports on the volatile components of E. ovalifolium.

Figure 1. Eriogonum ovalifolium var. depressum. A: Photograph by K. Swor at the time of collection. B: Scan of the pressed plant material.

2.   Materials and methods

2.1. Plant material

Aerial parts of E. ovalifolium var. depressum were collected on 8 May 2024 from three individual plants growing in Lake Owyhee State Park (Table 1). The plant was identified in the field by W.N. Setzer using a field guide [5] and verified by comparison with samples from the C.V. Starr Virtual Herbarium [6]. A voucher specimen (WNS-Eod-0119) was deposited in the University of Alabama in Huntsville Herbarium. The fresh plant material was stored frozen at (–20 °C) until distilled.

Table 1. Plant collection and hydrodistillation yields of Eriogonum ovalifolium var. depressum from southeastern Oregon

2.2. Essential oils extraction

The fresh-frozen plant material was hydrodistilled for four hours using a Likens-Nickerson apparatus with continuous extraction of the distillate with dichloromethane to give colorless essential oils (Table 1).

2.3. Gas chromatographic analysis

The E. ovalifolium var. depressum essential oils were analyzed using GC-MS, GC-FID, and enantioselective GC-MS as previously reported [7]. Retention indices were calculated using the method of van den Dool and Kratz [8]. Essential oil components were identified by comparison of mass spectral fragmentation patterns and retention indices found in the Adams [9], FFNSC3 [10], NIST20 [11], and Satyal [12] databases.

3.   Results and discussion

3.1. Essential oil composition

The colorless essential oils of E. ovalifolium var. depressum were obtained in relatively low yields (0.383-0.632%). Gas chromatographic analysis (GC-MS, GC-FID) allowed for the identification of a total of 82 components, which accounted for 98.3-100.0% of the total compositions (Table 2). The fatty-acid derivatives, n-alkanes (11.7-25.4%), fatty aldehydes (11.0-29.1%), and fatty acids (2.8-20.7%), were the dominant chemical class. Oxygenated sesquiterpenoids (12.3-15.9%) were also relatively abundant. The most abundant fatty acid derivatives were heptacosane (3.8-14.8%), pentacosane (3.6-7.9%), palmitic acid (0.0-11.5%), and (2E)-hexenal (4.9-12.9%). α-Turmerone (2.5-6.9%), β-turmerone (1.8-4.9%), and cis-ligustilide (2.6-7.9%) also had high percentages.

Since this is the first report on the essential oil composition of E. ovalifolium, there are no previous reports for comparison. Nevertheless, the essential oil composition of Eriogonum heracleoides Nutt. var. heracleoides has been described [13]. Fatty acid derivatives, fatty aldehydes in particular (33.5-60.0%), dominated the essential oils of E. heracleoides, including hexanal (2.3-3.8%), (2E)-hexenal (4.9-14.2%), nonanal (4.7-6.4%), dodecanal (2.8-7.4%), tridecanal (4.1-6.4%), and tetradecanal (2.5-4.7%). n-Alkanes (5.7-14.6%) and fatty acids (7.6-11.4%) were also abundant in E. heracleioides essential oil. Although the Polygonaceae is not regarded as an essential oil-producing family, investigations of the volatile compositions of members of the family have shown fatty aldehydes to be particularly abundant [13].

Table 2. Essential oil composition of three Eriogonum ovalifolium var. depressum samples from southeastern Oregon

RIcalc = Retention index determined with respect to a homologous series of n-alkanes on a ZB-5ms column. RIdb = Reference retention index obtained from the databases [9–12]. tr = trace (< 0.05%). a Reference RI on a 5% phenyl (polydimethylsiloxane) column not available.

3.2. Enantiomeric distribution of chiral monoterpenoids

Although monoterpene hydrocarbons made up a small proportion of the E. ovalifolium essential oil compositions (5.6-13.9%), enantioselective GC-MS was carried out, allowing the evaluation of the enantiomeric distributions of six monoterpenes (Table 3). α-Pinene was virtually racemic in the essential oils, but (–)-camphene (100%), (–)-β-pinene (85.4-100%), (+)-α-phellandrene (100%), (+)-limonene (78.0-80.0%), and (+)-β-phellandrene (100%) were the predominant enantiomers. This is the first report describing the enantiomeric distributions of monoterpene components of any Eriogonum species.

Table 3. Enantiomeric distribution of chiral monoterpenes in Eriogonum ovalifolium var. depressum essential oil from southeastern Oregon

RIdb = Retention index from our in-house database based on commercially available compounds available from Sigma-Aldrich and augmented with our own data. RIcalc = Calculated retention index based on a series of n-alkanes on a Restek B-Dex 325 capillary column. n.d. = not detected.

4.   Conclusions

This is the first report of the essential oil from E. ovalifolium. The essential oil was dominated by fatty acid derivatives, particularly n-alkanes and fatty aldehydes as well as fatty acids. These constituents seem to be common in the Polygonaceae and additional research on volatile components in members of the genus and the family should confirm this. However, essential oil yields were low, so E. ovalifolium cannot be considered a viable source of essential oil.

Authors’ contributions

Conceptualization, W.N.S.; Methodology, A.P., P.S., W.N.S.; Software, P.S.; Validation, W.N.S., Formal analysis, A.P., W.N.S.; Investigation, K.S. A.P., P.S., W.N.S.; Resources, P.S., W.N.S.; Data curation, W.N.S.; Writing – original draft preparation, W.N.S.; Writing – review & editing, K.S., A.P., P.S., W.N.S.; Project administration, W.N.S.

Acknowledgements

This work was carried out as part of the activities of the Aromatic Plant Research Center (APRC, https://aromaticplant.org/).

Funding

This research received no specific grant from any funding agency.

Availability of data and materials

All data will be made available on request according to the journal policy.

Conflicts of interest

The authors declare no conflict of interest.

References