Hypericum perforatum, commonly known as St. John's wort (sometimes perforate St. John's wort or common St. John's wort), is a flowering plant in the family Hypericaceae. It is a hairless, perennial herb with woody roots, yellow flowers marked by black glands, and leaves that appear perforated due to translucent glands, producing thousands of seeds per plant. H. perforatum is the type species of its genus, known for its historical use in folklore and traditional medicine. Probably a hybrid between the closely related H. attenuatum and H. maculatum (imperforate St. John's wort) that originated in Siberia, the species has spread worldwide. It can further hybridize with related species due to its allopolyploid nature. It is native to much of Europe, West and Central Asia, and parts of Africa and China and has been widely introduced elsewhere, thriving in well-drained, temperate habitats such as meadows, hillsides, and open woods with moderate rainfall and mild temperatures. It is a resilient, toxic, and invasive plant that reproduces sexually and vegetatively, supports specialized insect herbivores, suffers from plant diseases, and poses ecological and agricultural threats in many parts of the world. H. perforatum has been used for centuries in traditional medicine, especially for treating wounds and depression. To prepare it for use, the oil from its glands can be extracted or its above-ground parts can be dried and ground into a powder called herba hyperici. H. perforatum exhibits antidepressant effects comparable to drugs with fewer side effects for mild to moderate depression (for which it is approved in the European Union); however, it may interact with various medications by accelerating their metabolism.
Description
Hypericum perforatum is an herbaceous perennial plant with hairless (glabrous) stems and leaves. The root of each plant is slender and woody with many small, fibrous small side roots and also extensive, creeping rhizomes. The central root grows to a depth of 0.6–1.5 metres (2 ft 0 in – 4 ft 11 in) into the soil depending on conditions. The crown of the root is woody. Its stems are erect and branched in the upper section, and usually range from 0.3 metres to 1 metre in height. The stems are woody near their base and look like they have segmented joints from the scars left behind after the leaves fall off. The stems of H. perforatum are rusty-yellow to rosy in color with two distinct edges and usually have bark that sheds near the base. The stems persist through the winter and sprout new growth with flower buds in the following year; first year growth does not produce flowers. It has leaves that attach on opposite sides of the stems without a stalk (sessile). The leaves vary in shape from being very narrow and almost grass-like (linear), to a rounded oval slightly wider at the base with a rounded tip or not much of a tip (elliptic), or even narrow with the widest portion towards the end of the leaf like a reversed lance point, but still long and narrow (oblanceolate). The principal leaves range in length from 0.8 to 3.5 centimetres and 0.31–1.6 centimetres in width. Leaves borne on the branches subtend the shortened branchlets. The leaves are yellow-green in color, with scattered translucent dots of glandular tissue. The dots are clearly visible when held up to the light, giving the leaves a perforated appearance. The edges (margins) of the leaves usually have scattered black dots, often called dark glands, though sometimes they will appear away from the edges. The odor of the plant is faint, but aromatic, resembling that of resins like balsam. The taste of the plant is bitter and acrid.
Flowering characteristics
The flowers are conspicuous and showy, measuring about 1.5–2.5 cm (0.59–0.98 in) across, and are bright yellow with black dots along the edges of the petals. Each of the flowers normally has five large petals and five smaller leaf-like sepals below them. The sepals are about 4–5 mm (0.16–0.20 in) in length, green in color, are shaped like the head of a spear (lanceolate shape) with a pointed tip, and the same clear and black glands as the leaves. The petals are significantly longer, 8–12 mm (0.31–0.47 in) in length, and have an oblong shape. They completely hide the sepals from the front side of the flower. The many bright yellow stamens are united at the base into three bundles. The stalk portion of the stamens, the filaments, vary in length and stick out in every direction from the center of the flower. The pollen grains are pale brown to orange in color. Each flowering stem bears many flowers, between 25 and 100, and also is quite leafy. The fruit of Hypericum perforatum is a capsule 7–8 mm (0.28–0.31 in) in length containing the seeds in three valved chambers. Seeds that are separated from the capsules have a much higher germination rate due to an inhibiting factor in the capsule itself. The black and lustrous seeds are rough, netted with coarse grooves. Each seed is about 1 mm (0.039 in) in size. Each plant may produce an average of 15,000 to 34,000 seeds.
Similar species Hypericum maculatum is visually similar to Hypericum perforatum; however, its stems have four ridges instead of two and are also hollow. In addition, its leaves have fewer translucent glands and more dark glands. H. maculatum is native to the Old World but has also been introduced to North America. In North America several native species may be confused with Hypericum perforatum. Hypericum anagalloides is a low-growing creeping plant with rounder leaves and fewer stamens. Hypericum boreale is a smaller plant with more delicate flowers. Hypericum canadense has smaller flowers with sepals that show between the petals. Hypericum concinnum has flowers with petals that bend backward at the tip and also has much narrower, gray-green leaves. Growing in riparian areas along rivers, Hypericum ellipticum has wider leaves with a more elliptic shape. Hypericum scouleri has leaves that are broader at the base and also thicker. All except for H. concinnum grow in environments that are generally more moist than where H. perforatum is found.
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