The effect of provenance and species on the chemical composition of Epilobium herbal tea

Abstract

Background: Commercial herbal teas marketed as Epilobium herb are widely consumed in Europe for prostate-related and anti-inflammatory effects. However, they are often sold under generic names without clear species differentiation or quality specifications, raising concerns about chemical consistency and therapeutic equivalence. Objective: To evaluate the chemical equivalence of commercial Epilobium products and refine the framework for quality marker selection by integrating pharmacological relevance with structural assessment. Materials and Methods: Sixteen commercial tea samples labeled as E. angustifolium, E. parviflorum, E. hirsutum, from eight European countries were analyzed using high-performance thin-layer chromatography (HPTLC ) and validated by HPLC –DAD. Candidate markers were prioritized using the Herbal Chemical Marker Ranking System (Herb MaRS) and further assessed via Pan-Assay Interference Compounds (PAINS) structural filters. Results: Significant qualitative and quantitative heterogeneity was observed across all samples, including those labeled as the same species. Oenothein B was the dominant compound but exhibited high variability (7.9–48.7 mg/g DW; CV >50%) and was significantly higher in E. hirsutum (p < 0.05). Flavonol glycosides (e.g., hyperoside, isoquercitrin) also varied substantially. Although species identity influenced phenolic profiles, overlapping concentration ranges indicated a lack of chemical equivalence among products. Geographic origin contributed additional but secondary variability. Discussion: Oenothein B, hyperoside, and isoquercitrin were identified as priority quality markers based on abundance and analytical suitability. Structural reassessment demonstrated that pharmacological ranking alone may be misleading for polyphenol-rich matrices due to redox-related interference. Conclusion: Commercial Epilobium teas differ chemically and are not interchangeable. A structure-informed approach is essential for reliable quality assessment and for aligning commercial products with pharmacopeial standards.