Hypericum perforatum L.

Common St. John's-Wort

© SRTurner

Family - Hypericaceae

Habit - Perennial forb, the rootstock and stem bases often somewhat woody, often with short to long rhizomes.

	Roots and plant base.
© SRTurner

Stems - Ascending to erect, to 75 cm, sometimes multiple from base, the upper portion sharply ridged below each leaf, green to reddish brown, the surface often peeling in thin strips with age, glabrous.

	Stem and node.
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	Stems and leaves.
© SRTurner

Leaves - Opposite, decussate, simple, sessile. Blades 4-20 mm long, 2-8 mm wide, linear to narrowly oblong-elliptic, rounded to bluntly pointed or occasionally shallowly notched at the tip, narrowed or rounded at the base, the margins flat or somewhat rolled under at maturity, herbaceous in texture, with 1 or less commonly 3 main veins usually visible toward the base, the surfaces with few to many variously noticeable or inconspicuous yellowish brown to dark green or black dots or less commonly lines, or streaks, also with numerous pellucid dots, the upper surface green, the undersurface paler but only rarely slightly glaucous.

	Leaves.
© SRTurner

	Leaves abaxial.
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	Pellucid dots on leaves.
© SRTurner

Inflorescences - Appearing as panicles of 30-200 flowers, rounded to more or less flat-topped in outline. Pedicels 0 to 2 mm long, glabrous.

	Inflorescence.
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	Inflorescence.
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Flowers - Actinomorphic. Sepals 5, all more or less similar in size and shape, 3-6 mm long, narrowly lanceolate, the margins flat, with usually few noticeable black dots or streaks, these sometimes difficult to observe in fruiting material. Petals 5, 7-12 mm long, oblanceolate to obovate or elliptic, bright yellow, with yellowish brown or black dots present but usually relatively few and restricted to at or near the margins, withered and inconspicuous but usually persistent at fruiting. Stamens 45-85, the filaments fused into 3 groups toward the base. Ovary completely 3-locular (sometimes incompletely so at the very tip), the placentation axile. Styles 3, free above the base, more or less spreading, persistent, the stigmas capitate.

	Flowers.
© SRTurner

	Calyces.
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	Corolla. Black dots mostly confined to margins of petals.
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Fruits - Capsules 3.5-7.0 mm long, ovoid, widest below the midpoint, tapered to the minute beaks, bluntly triangular to more or less circular in cross-section. Seeds numerous, 0.9-1.2 mm long, the surface with a coarse network of ridges and pits, dark brown to black.

	Developing fruit, with 3 styles still intact.
© SRTurner

	Fruits.
© SRTurner

Flowering - May - September.

Habitat - Glades, upland prairies, forest margins, fields, pastures, levees, ditches, roadsides, railroads, open disturbed areas.

Origin - Native to Europe.

Lookalikes - H. punctatum.

Other info. - This species of St. John's wort is found throughout Missouri, as well as much of the eastern and western regions of the continental U.S. Plants in this genus are generally recognized by their opposite leaves having numerous translucent ("pellucid") dots, these being easily observed by holding a leaf up to a bright light source. This species is differentiated from others in the genus by having black dots along the margins of the petals (and not in the interior of the petals).

This is the species of Hypericum often sold as a herbal remedy under the name "St. John's wort." It has a long history of medicinal use, for indications too varied and numerous to list here. One prominent use has been as a treatment for depression. Clinical testing of St. John's wort for this indication has produced inconsistent results, possibly due to variable content of the active constituent(s) in the herbal preparations. The plant contains a number of non-alkaloidal secondary compounds including flavonoids, phenols, phloroglucinols, and anthraquinones, and the identity of the compound(s) responsible for the putative antidepressive effect is uncertain.

One effect of the plant which is well recognized is its induction of cytochrome P450 enzymes, which are bodily factors responsible for metabolizing and detoxifying exogenous small molecules. Induction of these can lead to abnormally rapid clearance of pharmaceutical medications, lessening their effectiveness. For this reason it is important to avoid consuming St. John's wort in combination with certain medications.

Another recognized effect of St. John's wort is toxicity to livestock, a problem which has resulted in the plant being classified as a noxious weed in several western states. Cattle, horses, and sheep which graze upon the plant develop swollen muzzles and ears, sores on their bodies, and a range of behavioral abnormalities. Some of these symptoms appear to be phototoxic in origin, manifesting following exposure to sunlight.

Photographs taken in Pictured Rocks National Seashore, MI., 7-22-02 (DETenaglia); also at Klondike County Park, St. Charles County, MO, 7-5-2013, in Spokane, Spokane County, WA, 6-13-2015, and near Loda Lake, Newaygo County, MI, 7-5-2023 (SRTurner).