Polyphenolic Fingerprint, Inter-Population Variability and Botanical Authentication of Wild Polygonum aviculare L. from Northwestern Romania

Polygonum aviculare L. (PAV) is a widely distributed medicinal plant traditionally used for its diuretic, anti-inflammatory, and antioxidant properties, whose phenolic composition varies with provenance. This study provides the first integrated pharmacobotanical and phytochemical characterization of five wild PAV populations collected across a lowland-to-mountain gradient (105–605 m a.s.l.) in Bihor County, northwestern Romania. Botanical identity was authenticated by macroscopic and microscopic pharmacobotanical examination, which revealed a consistent anatomical organization alongside a qualitative morphological gradient related to altitude. The phenolic profile of the aerial parts was determined by HPLC-DAD-ESI-MS, and differences among populations were assessed by one-way ANOVA with Tukey’s HSD test. Fourteen phenolic compounds were detected and annotated, comprising one hydroxycinnamic acid, twelve flavonol glycosides, and one flavonol aglycone, with kaempferol derivatives predominating across all populations. Chlorogenic acid and rutin were confirmed using authentic reference standards, whereas the remaining compounds were tentatively annotated. A quercetin-O-arabinoside tentatively assigned as avicularin was consistently detected across all populations, supporting its potential as a candidate phytochemical marker. The sum of chromatographically quantified phenolic compounds varied markedly, showing a nearly six-fold difference between the richest and poorest populations, while the qualitative fingerprint remained conserved. Exploratory analysis indicated a general tendency toward lower phenolic content along a lowland-to-mountain environmental gradient characterized by increasing altitude and precipitation and decreasing mean annual temperature, although the total content was not significantly correlated with altitude. This pronounced inter-population variability underlines that wild-harvested PAV cannot be assumed uniform, highlighting the need for standardized extracts and site-specific phytochemical documentation in its pharmaceutical use.