Common plants of the northern United States and Canada
reported to have caused poisonings, a dermatitis or hay fever in humans
Research Scientist and Research Institute Director (retired).
Honorary Research Associate (1987 - 2022), Agriculture and Agri-Food Canada,
Ottawa, Ontario K1A 0C6, Canada
Awarded the George Lawson Medal by the Canadian Botanical Association in 2006. Awarded the Faculty of Macdonald, McGill University, Most Distinguished Alumni Award on October 18, 2014.
Read his biography "The Real Weed Man" available in print and ebook.
This publication contains information on the common cultivated, native, and naturalized plants of the northern United States and Canada that are reported to have caused poisonings, a dermatitis or hay fever in humans. Much of the information given here was obtained during literature searches leading to the publication Poisonous plants of Canada, Agriculture Canada publication 1842/E, 1990, by Gerald A. Mulligan and Derek B. Munro. The severity of poisonings varies greatly from plant species to plant species, from person to person, and on the parts of the plant eaten. Some toxins are so potent that a single mouthful can cause severe poisoning, whereas others become toxic only after large quantities are consumed or when material is eaten over a long period of time. Plant poisons can cause only a slight discomfort in some cases, to a violent sickness or even death in others, depending on the species ingested and the susceptibility of an individual. People also differ greatly in their susceptibility to the different plants that cause a dermatitis and to the various plant pollens that cause hay fever, An attempt is made to provide some general information on the extent and severity of poisonings, dermatitis or hay fever caused by the ingestion or any other contact with various plant parts. More detailed information should be sought from local poison control centers, hospitals, educational institutions, and federal, state and provincial agencies.
Plant families, genera within each family, and species under each genus are listed alphabetically using the most widely accepted scientific names. Easy access to the scientific family containing information on any plant can be obtained by referring to the common name of the plant, listed alphabetically, in the following Links to families.
Refer to this web page for Information on plants, of Canada and the northern United States, that are reported to have poisoned livestock, or to have tainted animal products.
Refer to this web page for Additional information on hay fever plants
Links to families
autumn crocus- Liliaceae
black cherry- Rosaceae
black locust- Leguminosae
blue cohosh- Berberidaceae
bulbous buttercup- Ranunulaceae
English ivy- Araliaceae
false hellebore- Liliaceae
false indigo- Leguminosae
false ragweed- Compositae
gas plant- Rutaceae
giant hogweed- Umbelliferae
glory lily- Liliaceae
greater celandine- Papaveraceae
grasses- Gramineae (Poaceae)
grass pea- Leguminosae
Kaffir lilies- Amaryllidaceae
Kentucky coffeetree- Leguminosae
maidenhair tree- Ginkgoaceae
monk’s hood- Ranunculaceae
night-blooming jessamine- Solanaceae
ox-eye daisy- Compositae
poison sumac- Anacardiaceae
red chokecherry- Rosaceae
sweet pea- Leguminosae
Swiss-cheese plant- Araceae
tansy ragwort- Compositae
Virginia creeper- Vitaceae
white snakeroot- Compositae
wild calla- Araceae
wild ginger- Aristolochiaceae
wild parsnip- Umbelliferae
Information about plants causing poisoning, a dermatitis, or hay fever
Amaryllidaceae (amaryllis family)
L. and Amaryllis vittata
Ornamental herbs, usually grown indoors in our area.
Rare poisonings after the ingestion of bulbs.
species- Kaffir lilies
Small concentrations of certain alkaloids in the plants have caused, very rarely, a mild poisoning.
Rare poisonings caused by small concentrations of toxic alkaloids.
L.- narcissus, and
Narcissus pseudonarcissus L.-
Indoor and outdoor ornamentals.
Ingestion of bulbs has caused several hours of severe discomfort. Some people develop a skin dermatitis after handling large quantities of bulbs.
Anacardiaceae (cashew family)
The roots, stems, leaves and fruits of the following Toxicodendron species contain an oil that produces an irritating dermatitis in humans after an initial sensitization. Sensitivity to the poisonous oil varies greatly from person to person, and even during different periods in the same persons lifetime. Humans are not born sensitive to the oil, and therefore are not affected with the dermatitis on first contact with the plants. However, most people can be sensitized after a single contact. In general, children are more sensitive than adults, and people with a light skin react more than those with a pigmented skin. Since the poisonous oil must contact the cells beneath the skin layer, the dermatitis is most common and most severe in areas with thin skin. All of the following Toxicodendron species have clusters of yellow flowers and, later, whitish berries. Colored illustrations of all poisonous Toxicodendron taxa here.
(Torr. & Gray) Greene (=Rhus diversiloba Torr. & Gray-
Usually a trailing vine, confined to the extreme west coast of the United States and southern coast of British Columbia. Native to North America.
(L.) Kuntze subsp. negundo (Greene) Gillis [=Rhus radicans L. var. negundo (Gillis) G. A.
Mulligan- central poison-ivy
Usually a climbing vine; most common in in the north-central United States and extreme southern Canada.
subsp. radicans (=Rhus radicans var. radicans)- eastern poison-ivy
Usually a climbing vine; most common in the eastern United States and southeastern Canada. Native to North America.
subsp. rydbergii (Small ex Rydb.) Á& D.Löve [=Rhus radicans var. rydbergii (Small ex Rydb.) Rehd.]- rydberg’s poison-ivy
A trailing vine; most common in the northern United States and southern Canada.
(L.) Kuntze (=Rhus vernix L.)- poison sumac
Tall shrub to 20 feet (6m.) high; occasional in swamps and wet locations in the eastern United States, southern Ontario and southwestern Quebec.
Native tree in the northeastern United States and southwestern Ontario.
Contact dermatitis and severe gastrointestinal symptoms have occurred after the ingestion of fruits.
Apocynaceae (dogbane family)
Indoor ornamental climber.
Weak evidence exists that the fruit is poisonous.
androsaemifolium L.- spreading
dogbane, and Apocynum cannabinum L.-
Native herbs in the northern United States and southern Canada.
Sickness and death has resulted from their use for medicinal purposes.
There are many reports of poisonings and even deaths. Cases of dermatitis have been reported.
Aquifoliaceae (holly family)
The only reported case of poisoning is of a mild one, after two young children ate “a handful” of berries.
Araceae (arum family)
The leaves, stems, and roots of the following members of the arum family contain needle-shaped calcium oxalate raphide crystals. When eaten, these cause an intense burning sensation in the mouth and throat and the temporary paralysis of the throat muscles. This has resulted in the use of the common name dumbcane for the various species of Dieffenbachia.
House plants with us.
Native herb of eastern North America
Native herb throughout our area.
Gentil- giant dumbcane,
Dieffenbachia bausei Regel- dumbcane, and
Dieffenbachia picta Schott-
Indoor ornamentals with us.
Indoor ornamental climber.
House plants with us.
Can also cause a dermatitis on the skin of some people.
(L.) Nutt.- skunk-
A native herb in eastern North America.
Araliaceae (aralia family)
L.- English ivy
Outdoor and indoor ornamental.
Poisoning after the ingestion of leaves and berries has been reported, but none of the reports are recent. Some people develop a severe dermatitis after handling leaves.
Aristolochiaceae (birthwort family)
Native herb in southeastern Canada and the northeastern United States.
Some individuals develop a dermatitis after handling leaves.
thalictroides (L.) Michaux-
Native herb in southeastern Canada and northeast United States.
The berries and roots are cytotoxic.
Native herb in extreme southeastern Canada and in the northeastern United States.
There is only one report of poisoning, apparently from eating young shoots. Ingestion of fruits can cause a catharsis.
Boraginaceae (borage family)
Biennial herb, forming a flat rosette in the first year. Stems 1 to 3 feet (3 to 9 dm) high. Flowers bright blue. Widespread in the inland-east and rare elsewhere. Rocky permanent pastures, abandoned fields, meadows, and roadsides. Naturalized from Europe. Colored illustration can be viewed here.
Contact with the bristly hairs on the leaves and stems produces a severe skin inflammation and itching in some people.
Native herb in the mid-west.
Poisonings have occurred when used in herbal teas.
Campanulaceae (bellflower family)
Lobelia inflata L.- Indian-tobacco, and
Lobellia siphilitica L.- blue
Sickness and death has resulted when these plants were used for medicinal purposes in pioneer days.
Mild symptoms of feeling unwell and vomiting have resulted from eating berries or other plant parts of the following members of the honeysuckle family. Berries can be toxic if large quantities are eaten.
Native, naturalized, and ornamental shrubs.
Native, naturalized, and ornamental shrubs.
Native shrub found throughout most of our area.
Outdoor ornamental shrub or small tree; sometimes naturalized.
Celastraceae (stafftree family)
Jacq.- burningbush, and
Euonymus europaeus L.- European
Outdoor ornamental shrubs.
Mild symptoms have been reported to have occurred after eating berries.
Chenopodiaceae (goosefoot family)
Annual with stems 1 to 6 feet (3 to 18 dm) high, with inconspicuous green flowers. Widespread in cultivated land, grain fields, gardens, roadsides, and waste places. Naturalized from Europe.
Poisonings occurred in Europe when large quantities were consumed because of a serious food shortage in wartime.
Compositae [Asteraceae] (composite family)
Native, naturalized, and ornamental perennial herbs.
An allergic reaction, mainly affecting the eye area, can result from handling yarrows over a long period of time. Dairy products produced from cows grazing on common yarrow (Achillea lanulosa Nutt.) can have an undesirable flavor, but are not reported to be poisonous. Colored illustration of common yarrow can be viewed here.
Annual, stems usually 2 to 3 feet (6 to 9 dm) high; flowers inconspicuous, wind pollinated. Throughout most of our area, but most common in southern Quebec and Ontario and in the eastern United States. In cultivated fields, gardens, vacant lots, and especially along the fringes of roadsides. Native to North America.
Its wind-blown pollen is the most important cause of hay fever in eastern North America. However, there are many other plants with inconspicuous flowers and wind disseminated pollen that are potential causes of hay fever. As a general rule, plants with showy flowers produce small amounts of sticky pollen that adhere to insects and other flower visitors and is transferred by them to the stigmas of other plants, usually of the same species. Plants with inconspicuous flowers, usually have light pollen that is blown indiscriminately by the wind. This “wasteful” pollination strategy requires that the anthers on these plants produce large amounts of pollen. It is the plants with inconspicuos flowers, not those with showy flowers that cause most hay fever in humans.
Dairy products from cows that have grazed common ragweed often have an objectionable odor and taste, but I have found no reports that they are toxic.
Perennial with horizontal rootstocks; a smaller plant with rougher, thicker, and less lobed leaves than common ragweed, but otherwise similar; flowers inconspicuous, wind-pollinated; most common in the mid-west and west, but has recently spread eastward along railway beds; native to North America.
Its wind-blown pollen causes hay fever.
Annual, from 1 to 10 feet (3 to 30 dm) high; flowers inconspicuous, wind-pollinated. Most common in southwestern Quebec, southern Ontario, southern Manitoba and southward in the United States; roadsides, railway beds, agricultural fields, and waste places. Native to North America.
It is far less abundant than common ragweed, and its air-born pollen is less important as a cause of hay fever.
Perennial with stems to 5 feet (15 dm) high; flowers inconspicuous; plant strongly aromatic. Throughout our range, but particularly abundant in the mid-west; roadsides, waste places, farmyards, pastures, and cropland. Introduced from Europe.
Absinth is used in the preparation of some alcoholic beverages and was formerly used for medicinal purposes. Its volatile oils are toxic if consumed in large amounts.
Indoor and outdoor ornamentals.
An allergic dermatitis, affecting mainly the eye area, is an occupational hazard for some people who handle chrysanthemums over a long period of time. Similar allergic reactions can develop after prolonged contact with other members of the composite family. Sensitivity developed after prolonged contact with one species often results in an increased sensitivity to other members of the composite family.
Native herb of the eastern part of our area.
There are some early reports of sickness and death after drinking milk from cows that have eaten white snakeroot. However, there are no recent reports of any toxicity.
A persistent perennial with underground rootstocks; stems 6 to 8 inches (15 to 20 cm) high; flowers inconspicuous, wind-pollinated; common in the prairie region, less common in dry areas further west; native of North America.
Where abundant, its wind-blown pollen is an important cause of hay fever.
Annual; stems 3 to 8 feet (9 to 24 dm) high; flowers inconspicuous, wind-pollinated. Common in the mid-west, rare to the east and west; cultivated land, waste land, and gardens. Native to North America.
The abundant wind-blown pollen is an important cause of hay fever. Contact with leaves produces a dermatitis in some people. Milk from cows grazing this plant can have an undesirable flavor, but I have found no reports that it is toxic.
Perennial with stems 1 to 3 feet (3 to 9 dm) high; ray flowers white; disk flowers yellow. Throughout our area but rare in prairie regions; meadows, pastures, waste places, hayfields, and roadsides. Introduced from Europe.
Milk can have a disagreeable taste after this plant is eaten by cows. I have seen no indication that it is toxic.
Biennial or short-lived perennial with stems 1 to 3 feet (3 to 9 dm) high; flowers yellow; most common in eastern and western maritime areas, rare elsewhere. Pastures, hayfields, roadsides, and waste places. Introduced from Europe.
Poisoning has resulted from its use in herbal teas.
Ericaceae (heath family)
species- azaleas and rhododendrons
Native and ornamental shrubs.
Serious intoxications have occurred after children have eaten either leaves or flowers.
Ornamental shrub or small tree.
Ingestion of bark or roots has caused an irritation in the oral cavity and contact with the latex has produced an eczema.
The latex of all of the following species of the genus Euphorbia causes a dermatitis on the skin of most people and can cause sickness or death if ingested.
Perennial, with underground rootstocks; stems up to 1 foot (3 dm) high; flowering inflorescences yellow; locally common throughout most of our range, especially in the inland-east; roadsides, waste places, pastures, and open woods; often an escape from older cemeteries. Introduced from Europe as an ornamental.
Perennial, spreading mainly by its persistent, vertical and horizontal underground roots. Stems erect, from 1 to 3 feet (3 to 9 dm.) high. Flowering inflorescences from green to yellow. Locally common throughout most of our area, particularly the mid-west; grain fields, meadows, pastures, prairie, rangeland, roadsides, and waste places. Introduced from Europe and Asia.
Sporadically naturalized throughout our area.
Ornamental herb; sparingly naturalized in the coastal-west.
Ch. des Moulins-
Sparingly naturalized throughout our area.
Ingestion of only a few beans can cause poisoning or even death.
Severe dermatitis has resulted from handling broken or crushed fruits.
Gramineae (grass family)
Most members of the grass family have inconspicuous flowers that produce large amounts of wind-blown pollen that can cause hay fever in sensitive individuals.
Hippocastanaceae (horse-chestnut family)
Rare reports of children being poisoned after the ingestion of nuts.
Labiatae (mint family)
Sparingly naturalized throughout our area.
Some people have developed a dermatitis after contact with the leaves.
Seeds are used in necklaces and bracelets that are sometimes brought into our area by residents who have purchased them while traveling abroad.
The seeds are very poisonous. One ingested seed is often enough to be fatal even to a mature adult.
(L.) Br.- wild indigo and
Baptisia leucantha T. & G.-
wild false indigo
Perennial herbs, native to southern Ontario and southward into the United States.
Both plants are reported to be toxic.
(L.) K. Koch-
There is an 1898 report of a woman being poisoned as the result of eating the fruit pulp. I could find no other report of poisoning.
Ornamental shrub or tree.
Although it is considered the second most poisonous tree in Britain, I could find no documentation of fatalities.
L.- sweet pea (an
ornamental climber) and Lathyrus sativus L.- grass
pea (a food and forage herb)
Both species can cause serious poisoning if used habitually as a food source.
Native, naturalized, and ornamental herbs.
Mild poisoning has occurred after the ingestion of seeds.
Ornamental shrub or tree; sporadically naturalized.
Sickness is reported to have occurred after the ingestion of seeds and inner bark.
rhombifolia (Nutt.) Richards-
Native herb in the western half of our area.
Seeds have been implicated in the poisoning of children in Western Canada.
Woody ornamental climbers.
Children are reported to have been poisoned after the ingestion of seeds or pods.
Perennial house plants.
The latex present in the leaves can cause poisoning if ingested.
Indoor and outdoor ornamental.
Ingestion causes a burning sensation in the mouth and throat.
Ingestion of any plant part can cause sickness. The report that a child had died after drinking water in which this plant had been standing has been questioned by some authors.
Sickness and death has occurred after the ingestion of tubers.
Nausea and intestinal disorders have occurred in children after eating flowers.
Indoor and outdoor ornamental.
Some people develop a severe dermatitis, called tulip finger, after repeatedly handling large quantities of bulbs.
Native herb of the eastern part of our area and the extreme west.
Very poisonous. Sickness and even death will result from the ingestion of any part of this plant.
Pursh- white camas and
Zigadenus gramineus Rydb.-
Very poisonous. Sickness and even death has occurred after the ingestion of bulbs.
flavescens (Pursh) Nutt.-
Native south of our area. Sold around Christmas.
Mild poisonings, have been reported, after the ingestion of berries.
Menispermaceae (moonseed family)
Native in the southern part of our non-maritime east..
Poisoning and death has occurred after eating the grapelike fruits.
Moraceae (mulberry family)
(Raf.) C. K. Schneid.-
Small ornamental tree.
Some people develop a dermatitis after contacting the milky sap.
Oleaceae (olive family)
There are reports of the poisoning of children after the ingestion of berries. I have seen no documentation of these reports.
Orchidaceae (orchid family)
species- native lady’s-slippers
A dermatitis can result after contacting the glandular hairs on the plants.
Naturalized herb in the eastern part of our area.
Severe irritation and gastrointestinal problems are reported.
Toxic substances, that can cause poisoning if ingested, are present in the foliage and pods of many species.
Phytolaccaceae (pokeweed family)
Native herb of the eastern United States and extreme southeastern Canada.
Has caused severe poisonings when used as a folk medicine.
Polygonaceae (buckwheat family)
Perennial crop plant.
Sickness and death are reported to have occurred after the ingestion of large quantities of leaves.
Primulaceae (primrose family)
A severe skin dermatitis occurs in some people after contact with an irritant in the glandular hairs on the flower stalks and calyx.
Pteridaceae (fern family)
Perennial, with extensive creeping and forking underground rhizomes; fronds 3 to 15 feet (9 to 45 dm) high; throughout, except the mid-west; abandoned fields, open woods, swamps, bogs, burnt-over areas, grassy slopes, roadsides, and waste places. Native to North America.
Although sometimes eaten as a substitute for “fiddleheads”, recent evidence indicates that it can be carcinogenic.
Outdoor ornamental herb.
Very poisonous if ingested, especially the root.
Sparingly naturalized in the eastern part of our area.
Children have been poisoned from the ingestion of bulbous plant parts.
Rhamnaceae (buckthorn family)
L.-European buckthorn and
Rhamnus frangula L.- alder
Naturalized shrubs or small trees, introduced from Europe.
Rare cases of mild poisonings have occurred after eating fruits. The plants contain substances with laxative properties.
Rosaceae (rose family)
Ehrh.- black cherry and
Prunus virginiana L.- red
Native shrubs and small trees.
Poisoning and even the death of children has occurred as the result of them eating large quantities of fruits without removing the seeds.
Rutaceae (rue family)
Photosensitization can occur as the result of handling the plant, especially the seed pods; reddish patches can persist on the skin for weeks.
Illness has occurred after the ingestion of leaves or roots. Repeated handling of this plant by a nursery man resulted in a dermatitis on his hands.
Scrophulariaceae (figwort family)
Cultivated herb; sporadically naturalized.
Children have become sick after eating flowers, seeds, or leaves.
Simaroubaceae (quassia family)
A skin dermatitis can occur as the result of contact with the leaves.
Solanaceae (nightshade family)
Sickness has occurred after eating this plant.
Sickness and death have occurred as the result of eating plant parts.
Fresh leaves are toxic if eaten.
Woody climber; flowers purple; throughout, except mid-west; hedges, wood openings, and waste places. Introduced from Europe.
Berries are mildly poisonous, but serious illness has occurred after large quantities were eaten.
Naturalized herb scattered throughout most of our area.
Although sometimes eaten as a food, the fruit (especially unripe ones) can cause a serious illness.
Small ornamental shrub.
Nausea, abdominal pains, dilation of the pupils, and drowsiness, after eating its fruits has been reported.
Sickness and even death has occurred after eating large quantities of green-skinned potatoes or green fruits.
Taxaceae (yew family)
Native and ornamental shrubs; widely distributed.
Needles and seeds, but apparently not the flesh part of the berries, are toxic if ingested. Poisonings are rare.
Thymelaeaceae (mezereum family)
species- daphnes and
Poisonings are usually mild as few berries are eaten because of their acrid taste.
Shrub, native in eastern part of our area.
Some people develop a severe irritation and blistering of the skin after handling the bark of this plant.
The following water-hemlocks (Cicuta species) are extremely poisonous . Numerous sicknesses and deaths have been recorded. The most frequent poisonings have occurred after the ingestion of rootstocks.
(DC.) Coult. & Rose-
Native herb in the western part of our area.
Perennial with flowering stems 3 to 6 feet (9 to 18 dm) high; flowers white. Throughout our area. The most widespread of the three poisonous water-hemlocks. In wet habitats, especially along the margins of rivers, streams, and lakes. Native to North America.
Native in moist habitats in northern Canada and Alaska.
Biennial, with a disagreeable odor. Stems up to 6 feet (18 dm) high; flowers white. A very rare plant in our area. It occasionally grows in field borders, roadsides, and waste places. Introduced from Europe. Very poisonous. Sickness and death has occurred after the ingestion of leaves, roots or seeds.
mantegazzianum Somm. & Lev.-
Naturalized herb in southern Ontario and the adjacent United States.
A rash and persistent skin blisters can result when the handling of leaves is followed by an exposure to sunlight.
Biennial, with stems up to 3 feet (9 dm) high; flowers yellow; throughout, especially common in moist habitats in the non-maritime east; pastures, hayfields, ditches, riverbanks, roadsides, and waste places. Introduced from Europe.
Some people develop a severe dermatitis after having made contact with leaves, stems, or seeds.
Urticaceae (nettle family)
Native herb in the eastern half of our area.
A toxic liquid in in the stem hairs causes an intense itching and pain.
Perennial, with stems 1 to 8 feet (3 to 24 dm) high; flowers inconspicuous. Throughout our area; roadsides, waste places, and along margins of streams, rivers, and lakes. Both native populations and European introductions occur.
Contact with a toxic liquid in its sharp hairs will cause intense itching and pain.
Vitaceae (grape family)
quinquefolia (L.) Planch.-
Native climbing vine occurring in the eastern half of our area.
Ingestion of large quantities of berries can cause severe poisoning. The leaves contain raphides that will cause an irritation of the skin of some people.
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