POISONOUS PLANTS

William A. Dayton

PRACTICAL knowledge of the identity and actions of poisonous plants has been the possession of primitive peoples since time immemorial. Aboriginal folk everywhere are familiar with fish poisons, and the use of vegetable poisons on arrows by unlettered peoples is so general and widespread that it has given the modern science of toxicology (derived from the Greek toxon, bow, and its plural, toxa, bow and arrow) its technical name.

Published references to poisonous plants are of great antiquity. The ancient Egyptians were familiar with the toxic properties of aconite (Aconitum), henbane (Hyoscyamus niger) and poisonhemlock (Conium maculatum). About 900 B. C., in the fourth chapter of 2d Kings, we read that the famished "sons of the prophet," after partaking of a puree of "wild gourds" at Gilgal, cried out to Elisha "there is death in the pot!" Scholars are agreed that what these unfortunate gentlemen ate was the colocynth (Citrullus colocynthis), the colocynthis, or "colocynth apple," of our present-day drug trade. The prophet Amos complains that his countrymen "have turned the fruit of righteousness into hemlock." Xenophon, in the Anabasis, refers to the poisonous properties of an Asiatic rhododendron. The execution of Socrates ( 399 B. C.) with a cup of poison-hemlock, is a familiar incident both of bigotry and ancient toxicological lore. Probably the oldest extant treatise on poisonous plants is the poem Alexipharmica, by the Lydian priest-poet-physician, Nicander of Colophon (2d century B. C.) . after whom the poisonous ornamental apple-of-Peru genus (Nicandra) is named. The celebrated Greek herbalist, Dioscorides Pedanius (1st century A. D.) was familiar with the poisonous properties of ergot (Claviceps), autumn-crocus (Colchicum), the opium poppy (Papaver somniferum), and a number of other plants. Claudius Caesar, the Roman emperor mentioned in Acts 18: 2 as having banished the Jews from Rome, was poisoned A. D. 54 by his niece and wife, Agrippina, with a dish of toadstools (Amanita) in order to put her son Nero, by a former marriage, on the throne and, from this fact, Amanita Caesarea is thought to have derived its scientific name. Shakespeare has many references to poisonous plants : Hamlet's father's ghost tells his son that he was murdered with a vial of henbane; the witches in Macbeth add "root of hemlock digg'd i' the dark" to their "hell-broth" apparently alluding to European waterhemlock (Cicuta virosa), and darnel (Lolium temulentum), poisonhemlock, and fumitory (Fumaria officinalis) are referred to as noxious in the plays King Lear and Henry V.

Some common range stock-poisoning plants: A, Pingue (Actinea richardsonii); B, crazyweed (Oxytropis lambertii); C, Douglas waterhemlock (Cicuta douglasii); D, grassy deathcamas (Zigadenus gramineus); E, Menzies larkspur (Delphinium menziessi); F, tailcup lupine (Lupines caudatus).

Poisonous plants are an important consideration in livestock management, especially on range and native pastures. Annual losses in Colorado alone from this source are reported to average about a million dollars, and losses in the range country as a whole. from poisonous plants average about 4 percent annually. In addition, there is a considerable annual loss of human life from poisonous plants, particularly toxic fungi, and children are often tempted to eat elderberry (Sambucus) roots, raw horsechestnuts (Aesculus hippocastanum), water-hemlock tubers and the like, sometimes with fatal results. In this catalog of bad actors, the microscopic plants, particularly the bacteria, will not here be considered because of the lack of space.

A conservative estimate of the plants in this country known to poison domestic livestock or man is 62 families, 182 genera, and about 525 species. This list would easily run into four figures if every plant were considered about which some suspicion has been raised or which somebody somewhere has questioned. It disregards such plants as the potato, which, at certain stages, may contain toxic compounds, and ignores the numerous plants (such as species of Ceanothus and Cercocarpus) which are known to be important and valuable browse plants, but which, theoretically, are sometimes listed among poisonous plants because some chemical analysis has demonstrated some glucoside or other allegedly poisonous compound in some part. Admittedly, however, the list is still incomplete and scarcely a year goes by without adding some new culprit. The families with the greatest number of genera involved are, in order: Composites (daisy family), Liliaceae (lily family), legumes, spurges, heaths, crowfoots (buttercup family), umbel-lifers (parsnip family), milkweeds, grasses, and figworts. The four families with the greatest number of species involved are, in order: Legumes (easily first, with 102 species), crowfoots, composites, and spurges. Some families, such as the dogbane, milkweed, and spurge families, are notorious for their general possession of toxic properties, which are largely, in the families named, resident in their milky juices. In the case of some families, such as the lily and legume families, the poisonous properties are especially characteristic of certain tribes or other groups, as, for example, the asphodel, bunchflower, nolina and scilla tribes of the lily family, and the andromeda and rhododendron tribes of the heath family.

Some plants, harmless elsewhere, may become poisonous when growing on soils containing selenium because of their ability to substitute this toxic element for a harmless substance, such as sulfur, in their metabolism. In this category are the woody asters (Aster, sec. Xylorrhiza) crucifers of the genus Stanleya, timber poison-vetch (Astragalus convallarius), cultivated wheat, etc.

Aside from those plants, such as poison-ivy and nettles, which cause irritation or inflammation of the skin (dermatitis), probably the most common poisonous compounds in plants are (1) alkaloids, such as andromedotoxin, cicutin, cocaine, morphine, nicotine, and quinine these contain nitrogen, are the so-called "active principles" of plant compounds, and, in general, include the most virulent poisons; (2') glucosides, such as esculin (in the bark of horsechestnuts), and amygdalin (in the kernels of cherries and plums), which, under the action of an enzyme, acid, or other catalyst are broken down into sugars, alcohols, etc. In the latter category are an important group saponins, which are glucosides that have a soaplike action (saponify) in the presence of water. The common names of certain genera such as soapbark (Quillaja), soapberry (Sapindus), soapplant (Chlorogalum), soapweed ( Yucca spp.) , and soapwort (Saponaria) testify to the presence of saponin in certain of their tissues and make the parts of those plants toxic to some degree when taken internally.