Chemical Composition and Biological Activity of Hypericum Species—H. hirsutum, H. barbatum, H. rochelii

St. John's wort (<i>Hypericum perforatum</i>, Hypericaceae) is the most well-known species in the genus <i>Hypericum</i>, which comprises several hundred species. This study investigates the biological and phytochemical potential of the under-researched <i>Hypericum</i> species, <i>H. hirsutum</i>, <i>H. barbatum</i>, and <i>H. rochelii</i>. A high level of similarity between the chemical profiles of <i>H. hirsutum</i> and <i>H. barbatum</i> and the official source of the herbal drug (<i>H. perforatum</i>) 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 <i>H. hirsutum</i> extract, while the highest amount of flavonoids (47 mg QE/g) was recorded in <i>H. barbatum</i> 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 <i>S. aureus</i> was demonstrated for the tested species, with MIC/MBC values recorded at 12.5 µg/mL. Antifungal activity against <i>Candida</i> strains was not observed. The obtained results emphasize the need for further investigation of species of the genus <i>Hypericum</i> to discover potentially new sources of biologically active compounds.