The tomato, or nightshade family (Solanaceae), contains about 85 genera and 2,300 species. Most of the species are tropical or subtropical in distribution, and a few are of great economic importance. The region of greatest species richness is Central and South America, but representatives occur on all the habitable continents.
Plants in the Solanaceae family can be herbaceous annuals or perennials, shrubs, lianas (vines), or trees. They have alternate, simple leaves. The flowers are bisexual, meaning they contain both male (stamens) and female (pistil) organs. The flowers of most species have radial symmetry, and are pentamerous, meaning their flower parts occur in groups of five: there are normally five petals, sepals, pistils, and stamens. The individual flowers are aggregated into an inflorescence known as a cyme (a somewhat flat-topped cluster, in which the topmost flowers on the axis bloom first). The fruit is a many-seeded berry or a capsule.
Several species of Solanaceae are economically important food crops. The potato (Solanum tuberosum) is indigenous to the high plateau of the Andes region of South America, where it has been cultivated for at least 2,500 years. Wild potatoes have small, rounded, starchy, underground rhizomes known as tubers; these can weigh as much as several pounds (1 kg) in some domesticated varieties. Potatoes are a basic, carbohydrate-rich food, and are important in the diet of many people around the world. Another important cultivated species is the tomato (Lycopersicum esculentum), native to Central America and prized for its red, fleshy, vitamin-rich fruits (botanically, these are a berry). Less commonly eaten is the aubergine or eggplant (Solanum melongena), whose large, purplish, edible berry is usually eaten cooked. The numerous varieties of chili, or red pepper (Capsicum annuum), used to give a hot, spicy flavor to many foods, are also part of the Solanaceae family.
Other species of Solanaceae are used as medicinals and recreational drugs. Various species of thorn-apple (Datura species, including Datura stramonium of Europe and North America) are used to manufacture the alkaloid drugs scopolamine and hyoscine. The deadly nightshade (Atropa belladonna) provides similar alkaloids. The seeds and leaves of these plants are very poisonous if eaten. Tobacco (Nicotiana tabacum) is a widely used recreational drug, containing the extremely addictive alkaloid, nicotine.
Many species from the tomato family are used as ornamental plants because of their beautiful, colorful flowers. The most commonly cultivated plants are petunia hybrids (Petunia x hybrida). Also grown are the apple-of-Peru (Nicandra physalodes) and flowering tobacco (various species of Nicotiana).