FAMILY: Hypericaceae—the St John's wort Family
Native to temperate and tropical regions, this family of few genera has leaves: opposite or whorled, simple, entire, usually translucent-dotted or black-dotted; flowers: usually yellow, regular, bisexual; petals: separate; stamens: numerous, often united into clusters; styles: separate; fruit: a capsule.
PHENOLOGY: Hypericum perforatum flowers over an extended period, June through September.
DISTRIBUTION: The genus Hypericum provides several ornamentals for borders, rock gardens, ground-covers, or landscape shrubbery. H. perforatum has become an abundant weed of fields, meadows, roadsides, pastures, and waste places.
PLANT CHARACTERISTICS: Hypericum perforatum is a perennial, 4-8 dm, with many upright, leafy branches that are sharply ridged below the base of each leaf; leaves: linear-oblong, 2-4 cm on the main stem, half as long on the branches; inflorescence: cymose, flat topped, terminal; flowers: numerous; sepals: 4-6 mm, with few or no black dots; petals: 8-10 mm, black-dotted along the margin; stamens: in 3 clusters; styles: 3; seeds: 1-1.3 mm.
POISONOUS PARTS: All parts of the plant that bear the black dots, including petals and herbage, are poisonous.
SYMPTOMS: The black glands contain a toxin that is a primary phytophotosensitizer. These compounds are absorbed through the digestive system without alteration. In the circulatory system of mammals the chemicals damage the liver. In the presence of sunlight, skin develops dermatitis. Animals with normally dark pigmented skin are less likely to develop skin lesions. Hypericum perforatum produces intense dermal itching associated with aberrant behavior. Animals may experience convulsions prior to death. Often mucosa and eye epithelium are highly irritated. Blindness and starvation may precede death. Additional symptoms include elevated temperature, increased respiration and heart rate, and diarrhea.
Postmortem: gross lesions: dermatitis, conjunctivitis; skin lesions in cattle on teats, udder, and escutcheon; in sheep on head, ears, lips, eyelids, and coronet; skin changes proceed from reddening to edema, fluid weeps from the skin under necrotic tissue, and sloughs. In cattle, wounds heal slowly (approximately 2 weeks) and produce hairless scars. Death may result from infection and gangrene. Pyridine extracts of mouth, nasal and conjunctival mucosa, and digestive tract produce a light-red fluorescence under Wood's UV light; histological lesions: skin lesions including hyperemia, edema, necrosis. and ulceration.
POISONOUS PRINCIPLES: The toxic chemical probably is hypericin, a derivative of dianthrone. Previously, two substances, a volatile oil and hypericum red, were implicated. It has recently been suggested that a pigment, probably a mixture of numerous polyhydroxy derivatives of helianthrone, are responsible for primary photosensitization.
CONFUSED TAXA: More than a dozen species of Hypericum occur as native or naturalized plants in Pennsylvania; several additional species are cultivated in gardens. Although only H. perforatum is reported in the literature as poisonous, numerous other species produce black, glandular dots, which may prove to contain hypericin or related phytotoxins.
SPECIES OF ANIMALS AFFECTED: Humans, cattle, goats, sheep, and horses are reported to be affected.
TREATMENT: (11a)(b); (26); avoid direct sunlight after ingestion.
OF INTEREST: The active compound hypericin has a tonic and tranquilizing action on humans in very small quantities. Hay contaminated with dried St. John's wort is toxic since hypericin is stable upon drying and resistant to destruction by heat.