Common St. John's Wort

Scientific Name

Hypericum perforatum

Family

Hypericaceae (St. John’s worts) (sometimes placed in Clusiaceae)

Description

Native to Europe, common St. John’s wort mainly colonizes roadsides and other disturbed places in Missouri. It has a long history of medicinal uses that continues to the present day. It is one of 16 species of St. John's worts that occur in our state.

Common St. John’s wort is a shrublike, much branched, perennial herb, with sometimes woody stem bases, and leafy shoots.

The flowers are many, yellow, in flat or domed inflorescences. The petals are 5, broad at the base, with relatively few black dots (compared to other St. John's worts), usually at or near the margins; the sepals are with or without a few yellowish-brown to black dots.

Blooms May–September.

The leaves are many, crowded, and opposite; each pair is at right angles to those above and below (decussate), with many translucent spots; sessile (stalkless), linear to oblong, to 1½ inches long.

Similar species: There are 16 species of Hypericum recorded for Missouri, including two marsh St. John's worts (which in the past were placed in genus Triadenum). Some of our most common St. John's worts are natives:

Shrubby St. John’s wort (Hypericum prolificum): a woody shrub to 7 feet tall, scattered nearly statewide, with showy flowers; gaining popularity as an ornamental shrub.
St. Andrew’s cross (Hypericum hypericoides): a woody shrub from 4 inches to 2 feet tall (sometimes to nearly 5 feet), scattered in the southern half of Missouri; has 4-petaled, cross-shaped flowers that often are not very showy.
Nits and lice (Hypericum drummondii): an annual, scattered in all but the northwest quarter of Missouri. Has numerous upright branches, small, opposite, linear leaves, and small flowers; usually grows to about 15 inches tall.
Pineweed, or orange grass (Hypericum gentianoides): an annual, scattered in the southern half of Missouri. Has numerous upright branches and very small, scalelike leaves that are opposite and clasp the stem. The stems turn orangish with age and sometimes peel in thin strips. Looks like a very young pine.
Dwarf St. John’s wort, or small-flowered St. John's wort (Hypericum mutilum): usually an annual, scattered nearly statewide. The flowers are only ¼ inch across. Usually occurs in low, damp habitats.
Spotted St. John's wort (Hypericum pseudomaculatum): a perennial, scattered in the southwest quarter of the state. Very similar to H. punctatum.
Spotted St. John’s wort (Hypericum punctatum): a perennial, scattered nearly statewide. The sepals and petals are heavily covered with black dots.
Round-fruited St. John’s wort (Hypericum sphaerocarpum): a perennial, scattered nearly statewide. Lacks black spots or streaks on leaves and petals, but has tiny faint pale dots. Named for its nearly spherical capsules.

Other Common Names

Klamath Weed

Size

Height: to 3 feet.

image of Common St. John’s-Wort Klamath Weed distribution map

Scattered statewide.

Habitat and Conservation

Occurs in glades, prairies, and forest edges; also fields, pastures, levees, ditches, roadsides, railroads, and open, disturbed areas. In Missouri, this species mainly colonizes roadsides and other disturbed areas.

A native of Europe.

Status

Nonnative wildflower. Native to Europe. In Missouri, mainly colonizes roadsides and other disturbed areas.

In the western United States, a troublesome pasture weed; it is toxic to livestock.

Human Connections

In western states, this nonnative plant is a major weed of rangelands and is considered invasive. Pigment chemicals, including hypericin, which account for the dark dots on the petals and leaves, cause livestock to develop swollen mouths and ears and body sores upon sunlight exposure.

In Europe, this species has a long history of various medicinal uses. It was also believed to protect against witchcraft.

Modern studies have shown that the active ingredient, hypericin, is effective in treating mild to moderate depression. But check with your doctor, as it can interact with other drugs.

Ecosystem Connections

Like many weedy Eurasian plants, this species traveled with Europeans as they spread across the globe. In many countries, and some US states, it is a genuine invasive weed, outcompeting native plants and degrading native ecosystems. Its poisoning of livestock makes it even less welcome.

The genus Hypericum traditionally includes a group of plants that share many similarities: petals 4 or 5, yellow; stamens usually numerous; leaves opposite, simple, sessile, usually rather leathery, with entire margins; fruits usually oval or round capsules surrounded by the persistent sepals. In Missouri, most species live in open, relatively dry habitats.

A key feature of all the St. John's worts is their "glandular punctations": resinous or oil-bearing glands that appear as small dots when you hold the leaves up to the light. The dots can appear clear or dark, and they can occur on the stems, leaves, petals, and sepals.
Missouri has 16 species in genus Hypericum. Globally, there are 300 to 400 species in the genus.

The genus Hypericum has recently been expanded to include plants formerly segregated in genus Triadenum. Called marsh St. John's worts, these plants differ by having the petals pinkish (not yellow), and 9 stamens that are separated into 3 groups of 3, the filaments within each group of 3 fused toward the base.

Missouri's two species of marsh St. John's worts are Hypericum tubulosum and H. walteri. H. tubulosum is uncommon in the Bootheel lowlands. H. walteri is much more common than H. tubulosum, but it is still uncommon, occurring in the southeastern quarter of the state.

The St. John's wort family is the Hypericaceae (high-peer-uh-CAY-see-ee). Globally, the family has 6–9 genera, with about 700 species.

St. John's worts have sometimes been included in family Clusiaceae, and other times segregated into their own family, the Hypericaceae (as they are now). An old name for the Clusiaceae was "Guttiferae."

In the past, several plant families had names that were based on a description: the Compositae (aster family) for their composite flowerheads (now renamed family Asteraceae, for genus Aster); the Umbelliferae (carrot family) for their umbrella-shaped flower clusters (renamed as Apiaceae, for genus Apium); and the Cruciferae (mustard family) for their cross-shaped flowers (renamed as Brassicaceae, for genus Brassica).
The Guttiferae had been named for their guttiferous (resin- or oil-bearing) glands present in their leaves and other organs. The Hypericaceae is named for genus Hypericum. The Clusiaceae is named for genus Clusia (which does not occur in Missouri).