What is the scientific name of the plant commonly known as St. John's wort?

The scientific name of the plant commonly known as St. John’s wort is Hypericum perforatum.

Hypericum perforatum is a hairless, perennial flowering herb in the family Hypericaceae. Its yellow flowers have dark glands along their edges, while its leaves contain translucent oil glands that can look like tiny perforations when held up to light. That feature explains the species epithet perforatum, Latin for “perforated.”

The common name is linked to the midsummer flowering season. In European tradition, the plant was gathered around the feast of St. John the Baptist on June 24 and hung over doors or used in protective rituals. It was also called “witch’s herb” and “fuga daemonum,” reflecting older beliefs about its ability to repel evil.

A common mix-up is assuming every plant called St. John’s wort is Hypericum perforatum. The name can be used loosely for other Hypericum species, so “common” or “perforate” St. John’s wort is more precise. Extracts are widely marketed for mood-related uses, but they can interact seriously with medicines, including some antidepressants, contraceptives, and transplant drugs.