Heracleum lanatum Michx.—Cow parsnip
Heracleum mantegazzianum Sommier & Levl.—Giant hogweed
FAMILY: Umbelliferae (Apiaceae)—the Umbel Family (see Cicuta)
PHENOLOGY: Heracleum species flower throughout June and July.
DISTRIBUTION: Giant hogweed is native to the Caucasus Mountains and was cultivated in the U.S. as an unusual ornamental. Cow parsnip is a native plant growing in rich moist soil and low ground.
PLANT CHARACTERISTICS: The genus Heracleum contains plants that are tall, stout perennials with large compound leaves and broad, flat-topped, compound umbels with deciduous involucres and many-leaved involucels; corolla: white, peripheral flowers of the marginal umbellets irregular with the outer, bifid corolla-lobes enlarged; fruit: elliptic to obovate, dorsally strongly flattened, the lateral ribs broadly winged; oil-tubes 2-4 on the commissure, extending to about half-way down the fissure; leaves: lower ones, once pinnate; upper ones, once ternate.
POISONOUS PARTS: Upon contact, the herbage and fruits are highly irritating under the conditions described below.
SYMPTOMS: Giant hogweed produces severe, painful, burning blisters in susceptible people, the symptoms appearing within 24 to 48 hours after contact. The sap can produce painless red blotches that later blacken and scar the skin for several years. For an adverse reaction to occur the skin, contaminated with plant juices, must be moist and subsequently exposed to sunlight (see also Lantana and Hypericum). This phenomenon, known as phytophotosensitization, occurs in animals when chemical compounds, either derived directly from plants or produced by the animal in response to plant substances, are present in peripheral circulation. Heracleum lanatum has also been implicated in less severe photosensitization reactions in some people.
POISONOUS PRINCIPLES: The glycoside furanocoumarin is responsible for the severe contact dermatitis.
CONFUSED TAXA: Heracleum mantegazzianum is an herb that grows to 4 meters with leaves sometimes over 1 meter long, leafets: very large, deeply cut, green beneath; umbels: up to 1 meter across; petioles: blotched with purple, having large, coarse white hairs at the base; plants: coarsely hairy; flower stalks: ribbed. Heracleum lanatum is a smaller, less coarse (more softly pubescent) plant growing to 2 meters. Little or no purple markings are evident on the plant. Angelica atropurpurea, the purple-stemmed angelica, also a member of the Umbelliferae, has uniformly purple, hairless stems, and smaller, white-flowering flat-topped umbels less than 0.3 m in diameter.
SPECIES OF ANIMALS AFFECTED: Reports in the United States concern contact dermatitis in humans. However, photosensitization reactions can happen to livestock and pets.
TREATMENT: Washing sap-exposed skin with soap and water may help; where blisters appear: (4); (23); (26)
OF INTEREST: The recent detection of Heracleum mantegazzianum in Erie County provided the first record for this species in Pennsylvania. Other northern tier counties should remain alert for its presence; populations of the plant are known to occur 3 miles north of the Pennsylvania-New York border. It grows along roadside ditches and in moist waste areas. It has become naturalized in at least two dozen counties in central and western New York. Heracleum lanatum is reported to have medicinal properties and was once used for treating epilepsy.