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A plant is poisonous (Toxic) if it causes chemical injury to a person who either touches or swallows it, or in rare cases, breathes its scent. Harmful substances (Toxins) in plants are commonly classified by their effects upon victims, or their chemical structure:


Intoxication from imbibing beer, wine, or distilled liquor to the point of inebriation is one form of alcohol poisoning.

The breakdown of cabohydrates produces alcohol, although there are a few plants that produce toxic alcohols.

Two plants are found in Nova Scotia to contain toxic alcohols, water hemlock and white snakeroot (a rarely seen plant). Some consider the water hemlock to be the most poisonous plant of temperate North America.


Alkaloids are nitrogen-bearing alkaline chemicals that originate in plants. They are derived from amino acids, the building blocks of proteins, which especially affect the nervous system. At least 40% of all plant families include plants that contain these compounds.

Many plants have different alkaloids present, each with a specific activity. Some alkaloids are useful medicines; others are harmful, even fatal. Most are bitter tasting. The liver, with the assistance of enzymes, processes the alkaloids that enter the body, rendering some harmless there, while making others more toxic.

One common alkaloid, which many of us seek daily, is caffeine.

Carcinogens and co-carcinogens

A plant is identified as carcinogenic when it is shown to cause cancer in persons touching or eating it.

A plant is said to be co-carcinogenic when it causes cancer only in conjunction with some other substance. Roquefort and camembert cheese moulds, daphne, and poinsettias, for example, can cause cancer only if the victim eats them while taking certain prescription drugs.


Glycosides are toxins in which at least one sugar molecule is linked with oxygen to another compound, often nitrogen-based. They become harmful when the sugar molecule is stripped off, as in the process of digestion.

Hay Fever allergens

Some people develop sensitivities to the physical properties of some plants, especially seeds or pollen.

Pollen is produced by all flowering plants; it is essential to the fertilization of flowers. Some plants depend upon the wind to pollinate the flowers. Buoyant pollen grains, especially from trees and grasses, blow from plant to plant.

Not all wind-pollinated plants are toxic, but they tend to produce copious amounts of dust-like pollen. In susceptible people, this irritating pollen causes hay fever. Many plants cause hay fever—grasses, alders, poplars, birches, elms, and maples, to name a few. Not everyone reacts to all allergenic plants.

Hay fever results in influenza- or cold-like symptoms, with a definite seasonality to the condition. Spring sufferers of hay fever are probably allergic to tree pollen; early summer brings on reactions to grasses; and fall sufferers probably can’t tolerate ragweed.


Oxalates are unstable salts of oxalic acid. When eaten, they break down to release the highly poisonous acid.

The sour flavour of sorrel (Rumex species), wood sorrel (Oxalis), and even rhubarb is due to the presence of the acid.

Some plants may contain differing amounts of potassium or calcium salts, rendering them unsafe, particularly in the buckwheat and goosefoot families.


Phenols are acidic compounds that can stop all functions of living cells by altering or binding proteins. The most notorious phenol plant poison in Nova Scotia is the irritant found in poison ivy and its relatives, but phenols are also found in nettles.


Phototoxins are chemical substances that make the skin very sensitive to the ultraviolet radiation in sunlight and other light sources.

Proteins and Amino Acids

Proteins and amino acids are complex chemicals necessary to all living cells; most are highly beneficial, not harmful. Chains of amino acids form proteins; if more than two are joined, they are called peptides, rings of amino acids joined together make cyclopeptides like amanitins, some of which are the most deadly poisons known.

Resins and Volatile Oils

Resins and volatile oils are derived mostly from hydrocarbons—chemicals composed of hydrogen, carbon, and oxygen. This group of poisons is very diverse.

Shellfish Poisons

Shellfish poisoning occurs when filter-feeding shellfish (mussels, clams, oysters, and scallops) eat certain kinds of tiny marine algae. Toxins produced by the algae accumulate in the shellfish, making them poisonous when eaten.

In Nova Scotia, three main types of shellfish poisoning are known to occur: amnesic shellfish poisoning (ASP), diarrhetic shellfish poisoning (DSP), and paralytic shellfish poisoning (PSP). Generally, these are caused by marine algae called diatoms.



Poison Centre Information
Nova Scotia Museum