Chemical Composition and Biological Activity of Species-, , .

St. John's wort (, Hypericaceae) is the most well-known species in the genus , which comprises several hundred species. This study investigates the biological and phytochemical potential of the under-researched species, , , and . A high level of similarity between the chemical profiles of and and the official source of the herbal drug () was shown, but a higher content of quercetin and rutin was also found in all three evaluated species (116-230 µg/g dry herb). The highest amount of phenolics (195 mg GAE/g) was recorded in extract, while the highest amount of flavonoids (47 mg QE/g) was recorded in extract. The evaluated species were excellent scavengers of DPPH, OH, and NO radicals, as well as strong ferric ion reducers in the FRAP test. Prominent monoamine oxidase A and α-glucosidase inhibition was observed, compared to modest inhibition of monoamine oxidase B, α-amylase, and acetylcholinesterase. High activity against Gram-positive MRSA was demonstrated for the tested species, with MIC/MBC values recorded at 12.5 µg/mL. Antifungal activity against strains was not observed. The obtained results emphasize the need for further investigation of species of the genus to discover potentially new sources of biologically active compounds.