- Hypericum perforatum is a perennial, rhizomatous herb that can reach 4 ft. (1.2 m) in height.
- Leaves are opposite, sessile, elliptic, 0.4-1.2 in. (1-3 cm) long and dotted with many pellucid glands.
- Flowering occurs from June to September, when bright yellow flowers develop at the tips of the stems. Flowers have five petals and many stamens. Petals typically have black glands along the margins.
- The fruits are three-chambered capsules with three persistent styles.
- Ecological Threat
- Hypericum perforatum has been used to treat mild depression, but has been shown to cause hyper photosensitivity. Plants inhabit rangelands, pastures, roadsides and forest clearings. St Johnswort is native to Europe. Hypericum perforatum may be poisonous to cattle in large doses.
Zouhar, Kris. 2004. Hypericum perforatum. Fire Effects Information System, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory 
Oregon Department of Agriculture Plant Programs, Noxious Weed Control 
Washington State Noxious Weed Control Board 
Flora of China, www.eFloras.org 
California Invasive Plant Council 
USDA NRCS PLANTS 
USDA ARS GRIN 
Images from Bugwood.org