Nightshade is the common name for certain species of the plant genus Solanum. It is also the common name given to the plant family Solanaceae, of which the genus Solanum is part. The nightshade family includes several familiar food crops, such as potatoes, tomatoes and eggplants, all of which are also members of the genus Solanum but not commonly referred to as nightshade. The common name "enchanter's nightshade" refers to a group of unrelated plants in the genus Circaea of the family Onagraceae, while the common name "deadly nightshade" refers to a species in the related nightshade-family genus Atropa (A. belladonna).
Eight species of Solanum occur in Canada, of which only S. carolinense (horse or ball nettle), found in southern Ontario, is native. The most familiar nightshade found across Canada is S. dulcamara (climbing nightshade or European bittersweet). It is an attractive vine with potatolike purple or blue flowers and glossy, poisonous red berries, which occurs in a variety of different habitats.
Many nightshade species are extremely poisonous due to the presence of toxic alkaloids in various plant parts, including the foliage and berries. For example, S. americanum (black, American black or deadly nightshade) is poisonous to humans, browsing animals and poultry, causing similar symptoms such as paralysis and stupefaction. It need not be fatal, depending on the amount ingested and the maturity of the plant. Tubers of the closely related S. tuberosum (cultivated potato) are poisonous if they become green from exposure to sun, and the foliage and berries are also extremely toxic.
The nightshade family is important as a source of food, drugs and ornamental plants. It also contains many other poisonous plants. A. belladonna (Belladonna or "deadly nightshade") is a garden plant of Old World origin with poisonous black berries. Datura stramonium (thorn apple, jimsonweed, Angel Trumpet, Jamestown weed), native to Asia, is an ornamental and weed in North America with showy flowers and poisonous alkaloids in all plant parts; it is sometimes used recreationally as a hallucinogen. Tomato vines (Lycopersicon esculentum) are poisonous when grazed by cattle. Tobacco (Nicotiana spp) contains the toxic and addictive alkaloid nicotine.