The Phytochemical Potential of Viola Species, Melanium Subgenus, Subsection Bracteolatae

This study provides a comparative phytochemical evaluation of five Viola L. species belonging to the Melanium subgenus, subsection Bracteolatae: V. declinata, V. dacica, V. tricolor, V. arvensis, and V. kitaibeliana. Plant material was collected from natural populations in northeastern Romania, encompassing both alpine and agricultural habitats. We analyzed assimilatory pigments, anthocyanins, total phenolics, flavonoids, and antioxidant activity from aqueous and 50% ethanolic extracts (four plant-to-solvent ratios). Results showed that V. dacica and V. declinata, two Carpathian endemic taxa, had the highest contents of anthocyanins and phenolic compounds, which strongly correlated with their antioxidant activity. The quantitative analyses of total phenols for V. dacica were up to 94.81 ± 1.37 mg gallic acid equivalents/gram (GAE/g) (1% hydroalcoholic extract), and for anthocyanins were up to 113 ± 0.128 mg/g. Meanwhile, for V. declinate, total phenols were up to 95.53 ± 0.33 mg GAE/g (1% hydroalcoholic extract), and for anthocyanins, were up 0.909 ± 0.054 mg/g. V. kitaibeliana extracts, although obtained from lowland populations, were distinguished by elevated flavonoid concentrations, up to 56.61 ± 1.19 mg quercetin equivalents/gram (QE/g) dry biomass (0.5% hydroalcoholic extract). In contrast, V. arvensis and V. tricolor, cosmopolitan and widely used in traditional medicine, exhibited lower levels of bioactive compounds under the same extraction conditions. These findings highlight the pharmaceutical and ecological potential of less-studied Viola species and provide the first quantitative comparative data for V. dacica, V. declinata, and V. kitaibeliana. The results support the valorization of these taxa as valuable sources of bioactive secondary metabolites with antioxidant properties.