Maize , known as corn in some countries, is a cereal grain domesticated in Mesoamerica and subsequently spread throughout the American continents. After European contact with the Americas in the late 15th and early 16th century, maize spread to the rest of the world.

Maize is the most widely grown crop in the Americas (270 million tonnes annually in the United States alone). Hybrid maize, due to its high grain yield as a result of heterosis (“hybrid vigour”), is preferred by farmers over conventional varieties. While some maize varieties grow up to 7 metres (23 ft) tall in certain locations,[1] most commercially grown maize has been bred for a height of 2.5 metres (8 ft). Sweet corn is usually shorter than field-corn varieties.

Scientific classification
Kingdom:   Plantae
Division:     Magnoliophyta
Class:         Liliopsida
Order:        Poales
Family:       Poaceae
Genus:        Zea
Species:      Z. mays

The term maize derives from the Spanish form (maíz) of the indigenous Taino term for the plant, and is the form most commonly heard in the United Kingdom. In the United States, Canada and Australia, the usual term is corn, which originally referred to any grain (and still does in Britain), but which now refers exclusively to maize, having been shortened from the form “Indian corn” (which currently, at least in the U.S., is often used to refer specifically to multi-colored “field corn” cultivars).

Maize stems superficially resemble bamboo canes and the internodes can reach 20–30 centimetres (8–12 in). Maize has a very distinct growth form; the lower leaves being like broad flags, 50–100 centimetres long and 5–10 centimetres wide (2–4 ft by 2–4 in); the stems are erect, conventionally 2–3 metres (7–10 ft) in height, with many nodes, casting off flag-leaves at every node. Under these leaves and close to the stem grow the ears. They grow about 3 centimetres a day.

The ears are female inflorescences, tightly covered over by several layers of leaves, and so closed-in by them to the stem that they do not show themselves easily until the emergence of the pale yellow silks from the leaf whorl at the end of the ear. The silks are elongated stigmas that look like tufts of hair, at first green, and later red or yellow. Plantings for silage are even denser, and achieve an even lower percentage of ears and more plant matter. Certain varieties of maize have been bred to produce many additional developed ears, and these are the source of the “baby corn” that is used as a vegetable in Asian cuisine.

Maize is a facultative long-night plant and flowers in a certain number of growing degree days > 50 °F (10 °C) in the environment to which it is adapted.The magnitude of the influence that long nights have on the number of days that must pass before maize flowers is genetically prescribed and regulated by the phytochrome system.Photoperiodicity can be eccentric in tropical cultivars, while the long days characteristic of higher latitudes allow the plants to grow so tall that they do not have enough time to produce seed before being killed by frost. These attributes, however, may prove useful in using tropical maize for biofuels.

The apex of the stem ends in the tassel, an inflorescence of male flowers. Each silk may become pollinated to produce one kernel of corn. Young ears can be consumed raw, with the cob and silk, but as the plant matures (usually during the summer months) the cob becomes tougher and the silk dries to inedibility. By the end of the growing season, the kernels dry out and become difficult to chew without cooking them tender first in boiling water. Modern farming techniques in developed countries usually rely on dense planting, which produces on average only about 0.9 ears per stalk because it stresses the plants.

The kernel of corn has a pericarp of the fruit fused with the seed coat, typical of the grasses. It is close to a multiple fruit in structure, except that the individual fruits (the kernels) never fuse into a single mass. The grains are about the size of peas, and adhere in regular rows round a white pithy substance, which forms the ear. An ear contains from 200 to 400 kernels, and is from 10–25 centimetres (4–10 inches) in length. They are of various colors: blackish, bluish-gray, red, white and yellow. When ground into flour, maize yields more flour, with much less bran, than wheat does. However, it lacks the protein gluten of wheat and therefore makes baked goods with poor rising capability.

A genetic variation that accumulates more sugar and less starch in the ear is consumed as a vegetable and is called sweet corn.

Immature maize shoots accumulate a powerful antibiotic substance, DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one). DIMBOA is a member of a group of hydroxamic acids (also known as benzoxazinoids) that serve as a natural defense against a wide range of pests including insects, pathogenic fungi and bacteria. DIMBOA is also found in related grasses, particularly wheat. A maize mutant (bx) lacking DIMBOA is highly susceptible to be attacked by aphids and fungi. DIMBOA is also responsible for the relative resistance of immature maize to the European corn borer (family Crambidae). As maize matures, DIMBOA levels and resistance to the corn borer decline.