Maize (Zea mays L.) and all major cereal crops are members of the grass family, Gramineae. Worldwide, wheat, rice and maize are produced in greater quantities than any other crops. Of these crops, maize has the highest average yield per hectare (Table 1). Maize is third after wheat and rice in area harvested and total production.

Maize has the basic structure of the grass family (Figure 1), with conspicuous nodes and internodes on the stem. The leaves grow on opposite sides; one leaf per node. Maize is botanically unique among cereal crops. It is monoecious (separate male and female inflorescences on the same plant) and produces grains on lateral rather than terminal branches. Maize is a cross-pollinating (allogamous) species; therefore, a natural population is usually heterogeneous.

Crop	Area harvested (million ha)	Yield (t/ha)	Total production (million t)
Wheat Rice Maize	222 148 127	2.5 3.6 3.7	564 527 471

The origin of maize has been a matter of controversy. The most common opinion is that maize originated through domestication of the wild grass teosinte (Zea mexicana), which is native to Mexico, Guatemala, and Honduras.

Considerable cross-pollination between maize and teosinte has occurred during their evolution. However, since the two species differ considerably in appearance, some researchers maintain that maize must have originated from a wild pod corn that is now extinct. The first maize cobs that are still preserved are about 7000 years old and were found in a cave in Mexico.

By the time the Europeans reached the Americas, maize had attained its modern form and was a staple food throughout the western hemisphere. Maize spread rapidly to Europe, Africa, and Asia through the explorers of the 16th and 17th centuries.

Today, the United States grows nearly 40% of the total world production of maize and average yield is 7.5 t/ha. Much of the maize from developed countries is used for animal feed. Africa produces about 6% of the total world production, most of which is for human consumption. In West and Central Africa, average yield is about 1 t/ha, but higher (1.5-2 ton/ha) in East Africa, Asia, and Latin America

The maize plant has a remarkable productive potential. In 9 weeks in the lowland tropics, a single seed develops into a plant 2.5-3.5 m high. Two months later, it can produce 400-700 seeds.

The maize plant described in this document is representative of a lowland tropical variety, flowering in 55-60 days and maturing in 115 days.

However, considerable variation exists among varieties in morphology and growth habit. For example, an early-maturing tropical variety may reach a height of only 1.5 m, flowering in 45-50 days and maturing in 90 days. Furthermore, environmental factors influence the length of the various growth stages.