Poisonous plants

Poisonous plants

•Can be from:


–dermal contact



•“Poisonous” plants may be medicinal or food plants used improperly

•Nearly anything can be toxic given improper concentration


Plants synthesize chemicals

•Two basic parts of a plant's biochemistry:

•Basic metabolism, same for all plant species



–synthesis of cellulose, starches, proteins, lipids

Plants synthesize chemicals

•Secondary plant compounds

•Variable among species

•Include many defensive chemicals

•Two major groups that we will discuss



Plant toxins 

•Some toxins found throughout plant, some concentrated in certain organs

•Rhubarb contains oxalic acid throughout plant

•Petioles are safe to eat, but oxalic acid in leaves at higher concentration and can kill



•found in leaves, bark, unripe fruit, heartwood, roots

•easily bind with proteins to disable them

•in living tissues, plants store tannins in isolation to prevent damage to its own tissues

•gives unripe fruit astringent taste

•desired in tea, wine, cocoa

•used to "tan" animal skins

•deter insects, inhibit growth of fungi and bacteria


•bitter or toxic to many animals, prevents herbivory (animals eating plants)

•some used for traditional medicines, and as origins to at least 25% of modern pharmaceuticals

•pain relievers, cardiac and respiratory stimulants, muscle relaxants, blood vessel constrictors, cures for malaria, pupil dilaters



•caffiene in coffee and tea

•nicotine from tobacco

•cocaine from coca plant

•morphine and heroine from opium poppy

•many hallucinogens


Alkaloids in Solanaceae

•Solanine in members of family Solanaceae

•all but fruit and seeds of tomato plant



•green peppers

•deadly nightshade, source of belladonna

Alkaloids in Brassicaceae

•substance that impairs thyroid function

•blocks uptake of iodine

Poison oak and poison ivy

Poison oak and poison ivy

•Family Anacardiaceae

•all plants produce resin

•released to surface when plant is bruised

•50% of population has an allergic response (rash)

•10% of those are so sensitive that any contact requires medical attention

•cashews are in same family – beware of cross reactions

Water hemlock (Cicuta sp.)

•Extremely poisonous!!

•even small amounts can be fatal to humans or livestock

•all parts poisonous, especially chambered roots and base of stem


Zygadenus venenosus (Meadow death-camas)

•Flowers: Creamy white, foul-smelling and in a compact terminal cluster

•Bulbs and leaves can be confused with those of Camassia quamash and are extremely poisonous, as are the leaves.

•Strong alkaloid toxic to humans and livestock


•Cardiac glycoside

•can cause heart attack

•also used as heart medication

•slower and stronger heartbeat

•foxglove plants main source

Buttercup family


•contain Ranunculin

Delphinium (Larkspur)

•Contain delphinine (alkaloid)

•Toxic to cattle and humans

•Abdominal pain, nausea, depressed respiration and asphyxiation

Urtica dioica (stinging nettle)

•Stinging hairs are of hollow silica

•Contain formic acid

•Cause rash on exposed skin

•When cooked young shoots can be eaten

•Herbal remedy for allergies

•“If they would drink nettles in March / And eat mugwort in May / So many fine maidens / would not go to clay.”

Other plant defense mechanisms


–leaves and stems contain crystals of calcium oxalate

–if eaten cause swelling and pain in mouth and throat, loss of speech

•Odors or tastes to deter animals

–acrid, stinging, or hot and peppery

–doesn't prevent human herbivory

•Accumulation of minerals from soil

–copper, lead, cadmium, manganese, selenium, nitrates

–toxic to animals in sufficient quantities

•Lignin added to cell walls in woody plants for strength is indigestible to most animals