Forest Preserve District of Cook County, Illinois
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Poisonous Plants
Nature Bulletin No. 276   October 1, 1983
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

In the autumn of 1818, Nancy Hanks Lincoln died of milk sickness and left her son, Abe, motherless before he was ten years old. Since colonial times, in most of the eastern half of the United States, that dreaded disease has been a hazard in summer and fall, wherever cattle graze in woodlands or along wooded stream banks. In the 1920s it was finally traced to white snakeroot -- an erect branched plant, usually about 3 feet tall, with a slender round stem, sharply-toothed nettle-like leaves and, in late summer, several small heads of tiny white flowers. Cows eating small amounts over a long period develop a disease called "trembles", and their milk may bring death to nursing calves or milk sickness to humans. When larger amounts are eaten the cow, herself, may die.

Plants, ordinarily, are useful or harmless but a surprising number produce poisons. The U. S. Forest Service lists more than 500 species in this country but most kinds are poisonous only when eaten by man or domestic animals. In many cases, only one or more parts of the plant are poisonous -- perhaps only at certain seasons of the year or under certain conditions. The greatest danger to livestock occurs In early spring or in late summer and fall when pastures are scanty and the animals are tempted to eat weeds or leaves they otherwise avoid when tastier forage is plentiful. In the west, considerable losses among livestock are caused by many kinds of Locoweed which concentrate, in their leaves and stems, dangerous amounts of selenium and other poisonous minerals from the soil; also by many species of Wild Larkspur, and the Death Camass.

A few plants, like nettles, poison oak, and the poison sumac which grows in bogs, do not affect animals but cause severe rashes and blisters when touched by some people -- not all. Occasionally, people are found who are allergic to fruits such as strawberries or paw paws. or to foods made from buckwheat flour. Some develop a skin affliction from contact with the milky sap of the osage-orange tree, or certain plants of the spurge family.

Poisonous plants are scattered through many plant families in which most of their relatives may be harmless. Socrates was condemned to die by drinking a brew of Poison Hemlock, a member of the parsley family, now common in this country. The roots of the Water Hemlock, another common member, often mistaken for wild parsnip, are violently poisonous to humans and livestock. The fruits and generally the foliage of several members of the Nightshade family. Including Bittersweet and Jimson Weed, are poisonous.

The leaves of Johnson grass, sorghum cane, flax, and wild cherry trees contain a harmless substance which, when the leaves wilt, produces the fatal prussic acid. Several cultivated ornamental plants -- such as the lily-of-the-valley, larkspur, narcissus and English ivy -- are poisonous when eaten. So are some of our common wild flowers like the Dutchman's Breeches, Bouncing Bet, Skunk Cabbage and Jack-in- the-pulplt. The latter two have a pungent juice which painfully burns the mouth, throat and stomach but the Indians were able to destroy the poison and used these plants for food -- just as tropical Indians use the deadly cassava root from which we get tapioca.

There are several kinds of plant poisons, with different effects upon animals, including people. No one knows why they are produced by certain plants. Many, however, are also our sources of useful drugs such as quinine, digitalis, bella-donna, strychnine and morphine.

Maybe a dangerous weed is only a plant misused.

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