Seasonal variation of coumarin and flavonoid concentrations in persistent leaves of wyoming big sagebrush ( Artemisia tridentata ssp. wyomingensis: Asteraceae)

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Phenolic substances present in persisent leaves of 10 wyoming big sagebrush plants ( Artemisia tridentata Nutall ssp. wyomingensis Beetle & Young; Asteracae), growing wild from an unknown seed source were monitored over a two-year period to determine intraplant, interplant and seasonal variations in concentration using high performance liquid chromatography (HPLC). Phenolics in extracts of whole flowers were also monitored from early development to senescence during year two. Up to 36 compounds were separated in the extracts and the identified constituents included a large array of coumarins and flavonoids. Statistical analyses of the data indicated that 53% of the individual phenolics present in persistent leaves varied significantly over two years at P ≥ 0.05. However, during the four-month period of flower development, concentrations of only 39% of the phenolics varied significantly in persistent leaves. A posteriori tests performed on the 11 most highly variable phenolics over the two years showed that the variation in concentration occurs between seasons and not within. The results also revealed that intraplant variability was lower than interplant variation, and interplant variability in concentrations was generally equal to seasonal variability over two years. Thus, the observed seasonable changes of phenolic concentrations in persistent leaves were found to be relatively consistent and predictable both from season to season and from year to year.