Hypericum formosum - western St. john's wort

Family: Hyperiacea (Clusiaceae) - St. john's wort
Wetland Indictor Status: FAC

General Species Description

Hypericum formosum is a perennial herb that grows to about 2 ft in height. It has many leaves, and bright yellow flowers. The stems are round to slightly edged, especially near the base.


Leaves reach up to about an inch in length, are oval to oblong, opposite, and arranged as they ascend the styem in a rotating pattern, so that the pair of leaves above points in a different direction as those below. The leaves are grey-green underneath, and are covered with transparent dots which are apparent with held to the light. The prominent veins branching from the center vein of each leaf do so in the third nearest the stem. The leaf margins are entire.


H. formosum blooms July - September, producing bright yellow flowers that are 1 - 2cm in diameter, with 5 petals, each about 7mm in length. The petals, and the leaves as well, often have small, dark dots around their margins. There are 50 - 80 stamens in each flower, adn 3 styles per stigma.


The fruits are formed of a compound pistil with 3 segments. Seeds are veined and yellow to brown, and less than 1cm in length.


H. formosum thrives in moist, open sites, where it is able to compete with non-native weedy species such as himylayan blackberry (Rubus procerus). It is common in both scrub-shrub and emergent wetlands. --


Although some sources say that the plant is native to Europe, others describe it as being native to North America, where it is found along the west coast from British Columbia to California, and inland to Montana and Wyoming.

Similar Species

There are a number of Hypericum species that are similar to each other, and one in particular, klamath weed (H. perforatum), is difficult to differentiate from H. formosum. However, it is found in dry, gravelly, disturbed sites as opposed to wet ones and its leaves are more lance-shaped and its flowerheads more prolific than the formosum species. H. perforatum is also differentiated by the fact that it spreads by taproots, which H. formosum does not.

Ecological Value

For purposes of biological control, research in Australia has identified three European insect species that feed selectively on H. perforatum. Other than that, the specific ecological value is not known to the author.

Human Value

The injestion of any member of the Hypericum family typically causes weight loss and serious photosensitization in white-haired animals, including fair-complexioned people. However, it is a popular medicinal herb used to treat eye diseases, depression, and viruses, and to stimulate gastric and bile secretions. It is also used to counteract spasms, and to improve blood circulation and regulate menstruation. The maroon oil derived from its flowers can be spread on the skin to eliminate bruises.


Cooke, S.S, ed. 1997. A Field Guide to the Common Wetland Plants of Western Washington and Northwestern Oregon. Seattle Audubon Society and Washington Native Plant Society. Seattle Ausubon Society, Seattle, WA, 417pp. Dowden, Anne Ophelia. 1994. From Flower to Fruit. Ticknor and Fields, New York, 56pp. Hitchcock, Leo C. and Arthur Cronquist. 1973. Flora of the Pacific Northwest. University of Washington Press, Seattle, WA, and London, England, 730pp. Thomas, Patty, 1939 - , interviewed in Portland, OR on August 8, 1999. Whitson, Tom D., ed, 1996. Weeds of the West. Western Society of Weed Science in cooperation with the Western United States Land Grant Universities Cooperative Extension Services. University of Wyoming, 630pp.

This page was created by: Jorah Reinstein, August 1999

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