Common St. Johnswort or Klamathweed [Hypericum perforatum L.][HYPPE][CDFA list: C] Photographs

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SYNONYMS:klamathweed, goatweed, tipton weed, St. John’s wort

GENERAL DESCRIPTION:Erect noxious perennial, to 1.2 m tall, with rhizomes and showy, bright yellow flowers. Foliage is dotted with tiny translucent and black oil glands that contain hypericin, a fluorescent red pigment that is toxic to livestock when consumed in quantity, especially to animals with light-colored skin. Toxicity symptoms include skin photosensitivity of light-colored areas and loss of condition. Most animals graze plants only when more desirable forage is unavailable. In herbal medicine, hypericin is the antidepressant ingredient in St. Johnswort remedies. There are several regional varieties of common St. Johnswort. The variety in the Pacific Northwest is aggressively competitive and can spread rapidly by seed and rhizomes. By 1940, more than 2 million hectares (~ 1 million ha in California) of rangelands were infested. Several years later, the leaf-feeding flea beetles Chrysolina quadrigemina and C. hyperici and the root-boring beetle Agrilus hyperici were successfully introduced as biocontrol agents. Today infestations of the weed have been reduced by 97 to 99 %. Localized outbreaks of the plant sometimes occur after disturbances such as logging, fire, or during low population cycles of the flea and root-boring beetles. Introduced from Europe where it has been used medicinally for centuries.

SEEDLINGS:Cotyledons lanceolate to ovate, 1.5-3 mm long, 1-2 mm wide. Subsequent leaves opposite, oval to elliptic, increasingly larger. Underside leaf margins dotted with a few elevated black glands.

MATURE PLANT:Stems with numerous sterile shoots 2-10 cm long from the lower leaf axils, highly branched near the top, glabrous, often reddish, with black glands along 2 longitudinal ridges. Leaves opposite, elliptic-oblong to linear, 1-3 cm long, sessile, flat, glabrous, green, 3- to 5-veined from the base, dotted with numerous, tiny translucent glands that are visible when a leaf is held up to the light. Edges of leaf lower surfaces lined with elevated black glands. Margins rolled under (revolute).

ROOTS and UNDERGROUND STRUCTURES:Taproots stout, with many branched lateral roots, to ~ 1.5 m deep. Rhizomes develop just below the soil surface from the crown and can extend outwards to ~ 0.5 m. New shoots grow from the crown and rhizomes in early spring. Fragmented rhizomes can develop new plants. Under favorable conditions, roots grow deeper and fewer rhizomes develop. Specialized corky tissue (polyderm), found only in a few plant families, protects the roots and crowns.

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FLOWERS:June-September. Flowers bright yellow, ~ 2 cm in diameter, clustered at the stem tips. Petals 5, separate, 8-12 mm long, typically dotted with black glands along the margins. Sepals 5, linear-lanceolate, 4-5 mm long, much shorter than petals. Stamens yellow, numerous. Styles 3, 3-10 mm long. Plants typically do not flower the first year. Insect pollinated and apomictic (seed develops without pollination).

FRUITS and SEEDS:Capsules 3-chambered, ovate, not lobed, sticky-glandular, 5-10 mm long, with persistent styles 3-10 mm long, open longitudinally to release seed. Seed shiny black to brown, nearly cylindrical, ~ 1 mm long, densely pitted, often coated with gelatinous material from the capsule that aids dispersal and may inhibit germination until it breaks down or leaches out in about 4-6 months.

POSTSENESCENCE CHARACTERISTICS:Aerial growth dies back during the cold season. In forested or wildland areas, dry flower stems can contribute to fire hazard risks.

HABITAT:Rangeland areas and pastures (especially when poorly managed), fields, roadsides, forest clearings in temperate regions with cool, moist winters and dry summers. Grows best in open, disturbed sites and on slightly acidic to neutral soils. Does not tolerate saturated soils.

DISTRIBUTION: Northwestern region, Cascade Range, northern and central Sierra Nevada, Sacramento Valley, San Francisco Bay region, Central Coast, Peninsular Ranges; to Canada; Eastern U.S. To 1500 m (4900 ft).

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PROPAGATION/PHENOLOGY:Reproduces by seed and vegetatively from rhizomes. Plants can develop seed with or without pollination (facultative apomixis). Seed and capsules disperse with water and adhere to machinery, tires, shoes, clothing, and feet, fur, or feathers of animals. Seeds are hard-coated, and those consumed by animals remain intact and viable. Seeds from plants in the Pacific Northwest usually do not require an after-ripening period. Germination occurs fall through spring. Brief exposure to fire (100-140º C, 212-284º F) often increases germination. Calcium ions in water appears to inhibit germination of some biotypes. Seed can remain viable for ~10 years or more in the soil and for at least 5 years submerged in fresh water. Plants typically produce an average of 15,000-33,000 seeds per plant. Seedlings survive best on disturbed open sites.

MANAGEMENT FAVORING/DISCOURAGING SURVIVAL:Releasing the leaf-feeding beetle Chrysolina quadrigemina on uninfested plant populations can eventually give excellent long-term control. Cultivation readily controls plants on agricultural lands. Improving soil fertility and reseeding with desirable vegetation can help reduce or eliminate infestations in pastures. Mowing and overgrazing reduces seed production, but promotes vegetative spread from rhizomes. Burning stimulates seed germination and vegetative reproduction.

SIMILAR SPECIES:Dwarf St. Johnswort [Hypericum mutilum L.] is an uncommon erect annual to perennial to ~ 0.6 m tall that is distinguished by having petals +/- 2 mm long, sepals equal to or slightly longer than the petals, styles ~ 1 mm long, and 1-chambered capsules. Dwarf St. Johnswort occurs in moist places or riparian woodlands in the central-eastern Sacramento Valley and adjacent Sierra Nevada foothills to 300 m (1000 ft). It is introduced from eastern North America and expected to expand range. Canary Island St. Johnswort [Hypericum canariense L.][CalEPPC: Need more information] is an ornamental shrub with large flowers that has escaped cultivation in some places. Canary Island St. Johnswort grows to 4(5) m tall, has narrowly +/- elliptic leaves 2-7 cm long with wedge-shaped bases, sepals lined with hairs along the margins (ciliate), petals and stamens that persist after flowering, and leathery capsules that open at maturity. It occurs in disturbed places, coastal sage scrub, and grassland in the South Coast (especially San Diego area), to 100 m (330 ft). In addition, three native Hypericum species occur in roughly the same regions as common St. Johnswort. However, native species have at least one of the following characteristics: +/- prostrate habit with matted stolons, linear to lanceolate leaves with acute tips and usually folded along the midrib, sterile shoots at the base to 2 cm long, and 3-lobed capsules.

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