Conium maculatum L. —Poison hemlock; spotted hemlock; deadly hemlock; poison parsley
FAMILY: Umbelliferae (Apiaceae)—the Umbel Family (see Cicuta)
PHENOLOGY: Poison hemlock flowers June through September.
DISTRIBUTION: It is found in disturbed or waste areas such as roadsides and the edges of cultivated fields.
PLANT CHARACTERISTICS: Diagnostic features include, stem: purple-spotted, glabrous, and branched, up to 3 m tall; leaves: pinnately decompound, 2-4 dm long and toothed; flowering umbel: 4-6 cm wide (umbels are numerous); fruit: broadly ovoid, about 3 mm, laterally constricted; petals: white.
POISONOUS PARTS: All parts of Conium maculatum are extremely poisonous. Some studies reveal toxicosis at 0.25% (green-weight basis) of a horse's weight; 0.5% for a cow's. In contrast, experimental feeding studies on a cow showed symptoms at 2% of the animal's weight and produced death at about 4%.
SYMPTOMS: The symptoms, in order of appearance are: nervousness, weakness, trembling, ataxia, dilated pupils, weakened and slow heartbeat, drowsiness, nausea, vomiting, coldness in extremities or the entire body, labored respiration, paralysis, asphyxia, coma; death is due to respiratory failure. In animals the symptoms usually begin in the hind or lower extremities. The feces may be bloody and accompanied by gastrointestinal irritation and convulsions. Congestion of the respiratory tract is common. Symptoms occur within an hour after ingestion. Death is not always imminent. Abortion may result in pregnant animals. Milk from cows that have eaten Conium has an offensive flavor. Postmortem: gross lesions: widespread, passive congestion of lungs, liver, and nutrient myocardial vessels; histological lesions: cattle show severe mucoid or hemorrhagic enteritis.
POISONOUS PRINCIPLES: Gamma-coniceine, coniine, N-methylconiine, conLydrine, lambbaconiceine, and pesudoconhydrine. Toxicity levels vary with the stage of growth (time of year), plant part, and the plant's geographic location. The Conium alkaloids are similar in structure and function to nicotine. Gamma-coniceine appears to be the major alkaloid in the vegetative stage. Flowers and immature fruit contain coniine and N-methylconiine. In mature fruit the alkaloid is N-methylconiine. The root contains the least amount of toxins; mature seeds contain the greatest. It has been shown experimentally that the toxic principles in a plant vary even from hour to hour.
CONFUSED TAXA: Numerous members of the Umbelliferae superficially resemble Conium. Occasionally water-hemlock (see Cicuta) is confused with it. Cicuta has leaves organized into distinct and separate leaflets of uniform shape, often more than 2 cm wide. Conium has dissected leaves with the divisions under 1 cm wide. Conium can be confused with Daucus carota L. (Queen Anne's lace, wild carrot), which has distinctly hairy stems, petioles and leaves; poison hemlock stems are glabrous.
SPECIES OF ANIMALS AFFECTED: Humans and all species of livestock.
TREATMENT: (11a)(b); (20); (6); (2); short-acting barbiturates.
OF INTEREST: The odor of the plant, described as "mousy," may be detected on the breath and urine of animals that have eaten the plant. The drug coniine hydrobromide, derived from this plant, is used as an antispasmodic.