St John's wort (traditionally /ˈsɪndʒənzwɜrt/ SIN-jənz-wurt; now /wɔrt/ in some dialects) is the plant species Hypericum perforatum, and is also known as Tipton's weed, chase-devil, or Klamath weed.
With qualifiers, St John's wort is used to refer to any species of the genus Hypericum. Therefore, H. perforatum is sometimes called common St John's wort to differentiate it. The species of Hypericum are classified in the Hypericaceae family, having previously been classified as Guttiferae or Clusiaceae. Approximately 370 species of the genus Hypericum exist worldwide with a native geographical distribution including temperate and subtropical regions of North America, Europe, Turkey, Russia, India, China and Brazil.
St John's wort is widely known as an herbal medicine for treating mild forms of depression.
Read more about St John's Wort: Botanical Description, Ecology