I. Plants causing contact dermatitis.

Reference is Mitchell, John D. The poisonous Anacardiaceae genera of the world. IN New Directions in Study of Plants and People by Prance and Balick. 1990. Vol. 8 Advances in Economic Botany.
The best-known and most studied plants that cause contact dermatitis are members of the Anacardiaceae. A large number of species in this family cause this problem and the one you are probably most familiar with is poison ivy (Toxicodendron radicans). You are also probably familar with poison oak and poison sumac although they are not as common.
The chemicals which cause the reaction are phenolic compounds which are found in the oleoresins. The oleoresins are present in all plant parts with resin canals which is basically everything except pollen and stamens. The typical response is a cell-mediated, delayed, hypersenitivity reaction. The delay can be from 12 hours to 5 days. The oleoresins bind to skin proteins and this skin protein-oleoresin complex becomes the antigen that is recognized by the body's T-cells. Oleoresins can be spread by a number of vectors: direct contact, pets, smoke, sawdust. Internal ingestion of leaves and fruits can be fatal.

II. Fish poisons.

Reference is Acevedo-Rodriguez. The occurrence of piscicides and stupefactants in the Plant Kingdom. IN New Directions in Study of Plants and People by Prance and Balick. 1990. Vol. 8 Advances in Economic Botany.

Fish poisons are used to stupefy or kill fish without making them toxic to humans (hopefully). They are used most in Tropical America, Australasia and Tropical Africa, all regions of floristic richness. As with other useful aspects of plants, these poisons were probably discovered by accident, i.e., some plants used as soaps are rich in saponins, a common fish poison. It is possible a group took a bath in a still pool and noticed that dead or stunned fish started coming to the surface.

These poisons are usually used in small rivers or pools with slow-moving water. Their use can be tricky since too much poison could kill all the fish in an area or make them too toxic to eat. The poisons are prepared in a number of ways. The simplest is to crush plants with a rock and throw them in the water. Some poisons are incorporated into food to make a bait but this is more likely to make the fish toxic. The plants may also be cooked or fermented, depending on the toxic principle.

Summary table of fish poisons.

Active principle - Mode of action - Families
1. Rotenone - Interferes with respiration - Fabaceae
2. Saponins - Asphyxiation - Sapindaceae
3. Cardiac glycosides - Affect CNS and nerve mechanism of heart - Apocynaceae, Moraceae, and Ascledpidaceae
4. Alkaloids - Many affects - Solanaceae, Ranunculaceae
5. Tannins - Very slow-acting - Many families
6. Ichthyoethereol - Interferes with respiration - Asteraceae
7. Cyanogenic compounds - Produce HCN - Rosaceae, Euphorbiaceae

"Fish poisons" have also been used as soap, medicines, insecticides, antitumor agents, arrow poisons and molluskicides.

III. Partial listing of poisonous plants. The following plants were taken from Poisonous Plants of the United States and Canada by Kingsbury and the AMA Handbook of Poisonous and Injurious Plants. The listing below is by family and is not intended to be comprehensive. The plants in the list have varying levels of toxicity, some are deadly in small amounts, some are harmless under most circumstances. If a plant is exposed to large amounts of nitrate (through fertilization), it may accumulate in the plant to levels that are toxic to animals that eat large amounts of these plants. So, sometimes the plants are not inherently toxic but cause problems due to external factors. This often occurs in weeds of agricultural areas.

Lauraceae - Persea americana - Avocado. Leaves, fruit and seeds are poisonous to animals. The name avocado comes from Aztec word which testicle tree (the fruits hang in pairs)

Ranunculaceae - This family contains many poisonous members.
Aconitum - Monkshood, very poisonous
Caltha palustris - Marsh marigold
Delphinium - second only to locoweeds in livestock poisonings in Western U.S.


Papaver somniferum

Fagaceae - tannin poisoning from members of Quercus

- Injestion of large amounts can be fatal due to mustard oils.

Malvaceae - Cotton seed contains gossypol, which causes problems with swine and poultry.

Euphorbiaceae - Many toxic species
Croton - croton oil is a strong purgative
Euphorbia - many are toxic
Ricinus commonus - castor beans, castor oil is used as a laxative but does not contain the toxic substance found in the seeds, ricin, which is one of the most toxic substances known.

Phytolaccaceae - Phytolacca americana roots and leaves are toxic

Rheum (rhubarb) leaves are occasionally reported to be toxic, the petioles are ok.
Rumex (dock)- occasional poisoning due to high oxalate content.

Ericaceae - Kalmia and Rhododendron can cause serious poisoning of sheep.

Fabales - contains large number of toxic species, many of which are serious problems for livestock

Abrus - Rosary pea - 1 seed can be fatal
Astragalus and Oxytropis are "locoweeds" and cause large losses of livestock
- Mesquite

Rosaceae - cyanogenic compounds are high in the leaves of some members of this family. The most common one encountered in this country is Prunus serotina.

Cicuta maculata - Water hemlock, native to U.S.
Conium maculatum - Poison hemlock, cultivated for fernlike foliage.

Asclepiadaceae - Many members of this family are toxic, cardiac glycosides are often the culprit.

Solanaceae - members of this family produce a wide array of alkaloids
Atropa belladonna - deadly nightshade, European native, cultivated in U.S., active compound is atropine, which is also a useful drug.
Datura - Jimsonweed
Lycopersicon - foliage and vines are toxic
Nicotiana - tobacco

Verbenaceae - Lantana - poisoning caused by immature berries

Castilleja - Selenium accumulator
Digitalis purpurea - foxglove

Lobelia - contains alkaloids

Asteraceae - members of this large and diverse family produce alkaloids and sesquiterpene lactones (many of which cause contact dermatitis).

Eupatorium rugosum - Snakeroot - milk disease in humans is caused by drinking milk of animals feeding on this plant
- causes milk to be bitter
Senecio - very large genus that produces alkaloids and sesquiterpene lactones
Xanthium - cocklebur

Araceae - Mostly tropical family, many members of which are used as house plants. Plants contain calcium oxalate and other toxins. Most common symptom is swelling of tongue. These plants should be kept out of the reach of small children and pets.

many others

- Sorhgum halepense (Johnson Grass) - cyanide poisoning, especially dangerous after a freeze

Amianthum - fly poison
Colchicum - Crocus - produce colchicine (alkaloid) which is a mutagen, probably a carcinogen, disrupts mitosis.
Veratrum - False Helebores - produce many alkaloids
Zigadenus - Death Camas - toxic alkaloids

Agave lecheguilla - photosensitization, kidney and liver damage, compound is saponin.

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