Allium is a genus of monocotyledonous flowering plants that includes the cultivated onion, garlic, scallion, shallot and leek as well as chives and hundreds of other wild species. The generic name Allium is the Latin word for garlic, and Linnaeus first described the genus Allium in 1753. Various Allium have been cultivated from the earliest times and about a dozen species are economically important as crops, or garden vegetables, and an increasing number of species are important as ornamental plants. Estimates of the number of species have been about 750 species. They vary in height between 5 cm and 150 cm. The flowers form an umbel at the top of a leafless stalk. The bulbs vary in size between species, from small (around 2–3 mm in diameter) to rather large (8–10 cm). Allium species occur in temperate climates of the Northern Hemisphere, except for a few species occurring in Chile, Brazil, and tropical Africa.
The cooking and consumption of parts of the plants is due to the large variety of flavours and textures of the species. In most cases, both bulb and leaves are edible and the taste may be strong or weak, depending on the species and on ground sulfur (usually as sulfate) content. Plants of the Allium genus produce chemical compounds (mostly derived from cysteine sulfoxides) that give them a characteristic (alliaceous) onion or garlic taste and odour.