Hypericum is a genus of flowering plants in the family Hypericaceae (formerly often considered a subfamily of Clusiaceae). Hypericum is unusual for a genus of its size because a worldwide taxonomic monograph was produced for it by Norman Robson(working at the Natural History Museum, London). Robson recognizes 36 sections within Hypericum. The genus has a nearly worldwide distribution, missing only from tropical lowlands, deserts and polar regions. All members of the genus may be referred to as St. John’s wort, and some are known as tutsan. The white or pink flowered marsh St. John’s-worts of North American and eastern Asia are nowadays separated into the genus Triadenum.