The Essential Oils of Wyethia Species: Wyethia Amplexicaulis (Nutt.) Nutt. and Wyethia Helianthoides Nutt.

Background/Objective: Wyethia amplexicaulis (shiny mule's ears) and Wyethia helianthoides (white-head mule's ears) are conspicuous forbs growing in open hillsides and prairies at mid to upper elevations in the Intermountain West region of the United States. There have been no previous reports on the essential oil compositions of any Wyethia species, so the objective of this study is to examine the chemical compositions, including enantiomeric distribution of chiral terpenoids, of W. amplexicaulis and W. helianthoides from southern Idaho. Methods: Three individual samples of W. amplexicaulis and W. helianthoides were collected, and the essential oils were obtained by hydrodistillation using a Likens-Nickerson apparatus and analyzed by gas chromatography coupled with mass spectrometry (GC-MS), gas chromatography with flame ionization detection, and enantioselective GC-MS. Results: The essential oils were obtained in yields of 0.090% to 0.136% and 1.489% to 1.771% for W. amplexicaulis and W. helianthoides, respectively. The three W. helianthoides samples showed high similarity with (−)-germacrene D (16.5%-21.5%), ( E)-β-ocimene (10.0%-14.3%), myrcene (8.6%-12.4%), α-pinene (6.3%-7.3%, ≥ 95% (+)-α-pinene), 15-copaenol (4.3%-6.0%), and carotol (3.5%-5.9%) as the major components. The W. amplexicaulis essential oils, on the other hand, showed variation. Two samples were rich in monoterpene hydrocarbons, mostly myrcene (22.4% and 32.2%), while the third sample was dominated by oxygenated sesquiterpenoids, 15-copaenol (11.4%), carotol (10.0%), silphiperolan-7β-ol (8.2%), and caryophyllene oxide (5.8%). This is the first investigation of Wyethia essential oils. Conclusions: There are 11 recognized Wyethia species, so additional research is needed to understand the volatile phytochemicals present in this genus.