Light micrograph (LM) of St. John's Wort crystals. St John's Wort used alone refers to the species Hypericum perforatum, also known as Klamath weed or goat weed, but it can be used to refer to any species of the genus Hypericum. It is a yellow-flowering, rhizomatous, perennial herb indigenous to Europe, which has been introduced to the Americas and grows wild in many meadows. The name comes from the fact that it traditionally flowers by and is harvested on St John's day; all above-ground parts are cut and dried for later use in the form of herbal tea, which has long been enjoyed both for its taste and for its medicinal properties. The first recorded use of Hypericum for medicinal purposes dates back to ancient Greece, and it has been used ever since. In modern medicine it is commonly used as a treatment for depression and anxiety disorders. Magnification: x40 when shortest axis printed at 25 millimetres.
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