Common St. John's wort is a weedy perennial which reproduces via seeds or short runners. The numerous erect and branched stems arise 30-90 cm high. The stems are rust-colored and somewhat woody at the base. The leaves are opposite, sessile, entire, and elliptic to oblong. They are not over 3 cm in length, and they are covered with transparent dots.
The flowers are numerous in flat-toped cymes. The 5 green sepals are lanceolate with pointed tips, and range from 5-7 mm long. The 5 yellow petals are about twice as long as the sepals. The margins of the petals may have numerous black spots. The 75-100 stamens seem to be bundled into 3, or occasionally 4 or 5 groups.
Common St. John's wort contains a toxic substance which affects white-haired animals. Although the animals rarely die, they will lose weight and will develop a rash when exposed to strong sunlight. Several European insects have been introduced into the west as control of the plant, and have seen partial success.
Common St. John's wort may be found on disturbed roadsides, waste land, and pastures. It tends to be found in open, drier places. In the Pacific Northwest, it seems abundant on sandy or gravelly soils.
Common St. John's Wort is an introduced European weed, now a serious pest throughout much of the U.S.. It is common west of the Cascades and Sierra Nevada from Tacoma, WA south to central California, and less so to British Columbia and east to Montana.
In the Columbia River Gorge, it may be found between the elevations of 0'-4000' throughout the length of the gorge.
- 
