Maize (Zea mays), commonly called corn, is an annual cereal plant of the grass family, Poaceae. Cultivated maize belongs to the subspecies Zea mays subsp. mays. Domesticated by Indigenous peoples in Mexico, it is now grown worldwide for its grain and other plant material. Its uses include human food, livestock feed, starch, oil, sweeteners, and fuel ethanol. Maize is the world's largest cereal crop by harvested grain weight. (powo.science.kew.org)
Origins and dispersal
Maize domestication began approximately 9,000 years ago in southwestern Mexico, principally from teosinte, a group of wild grasses closely related to cultivated maize. Archaeological evidence from the central Balsas River valley includes maize starch grains and microscopic silica structures on stone tools associated with deposits dating to about 8,700 calendar years before present. These remains establish that maize grain was already being processed during that period. (pmc.ncbi.nlm.nih.gov)
Cultivation spread through the Americas long before European contact. Archaeological records document maize in Panama by approximately 7,600 calendar years before present and its establishment in northwestern South America by around 6,000 years before present. It subsequently became an important crop in numerous Indigenous agricultural systems. Introduced to Europe through Spain after the transatlantic voyages of the late fifteenth century, maize later spread into Africa and Asia. (pmc.ncbi.nlm.nih.gov)
Maize also acquired religious and cultural significance, notably among Maya peoples. In the agricultural practice known as the Three Sisters, maize is grown alongside beans and squash, combining crops with different growth habits and food uses. (kew.org)
Structure and reproduction
The maize plant has an upright stem with elongated leaves arranged alternately along it. Male flowers form the terminal tassel, while female flowers develop in ears situated at leaf axils. The ears are enclosed by husks, and their flowers produce long threadlike silks that extend beyond the husk tips. Kernel colors include white, yellow, red, purple, and black. (kew.org)
Pollination is predominantly wind-mediated. Each silk connects to an individual ovule that can develop into a kernel after fertilization. Successful kernel formation depends on the overlap between pollen shedding and silk emergence. Environmental stress that delays silk growth can reduce fertilization and leave parts of an ear without kernels; subsequent stress can also cause developing kernels to abort. (ag.purdue.edu)
Botanically, the kernel is a caryopsis, the characteristic grain fruit of grasses. Its main components are the outer pericarp, the endosperm, and the germ or embryo. The endosperm normally constitutes approximately four-fifths of kernel weight and stores most of its starch. The germ contains much of the oil, while the outer tissues contain substantial fibrous material. (fao.org)
Physiology and cultivation
Maize uses C4 photosynthesis, a carbon-concentrating pathway associated with efficient growth under warm, well-lit conditions. FAO crop profiles place optimum photosynthesis and growth broadly between 20 and 30°C, although requirements differ among cultivars. Growing periods vary considerably: some temperate and tropical lowland cultivars mature within roughly 90–180 days, whereas highland types may require substantially longer. (s3.eu-west-1.amazonaws.com)
Despite comparatively high water-use efficiency, maize remains sensitive to water shortage, particularly around flowering and early grain development. Yield depends on the interaction of cultivar, temperature, water availability, soil conditions, and crop management. Irrigation can supplement rainfall where necessary, but many production systems are rain-fed. (fao.org)
Breeding programs select for grain yield, maturity, stress tolerance, nutrient-use efficiency, and nutritional quality. Their testing distinguishes performance under favorable conditions from performance under drought, disease pressure, or other stresses, because a line successful in one environment may not perform equally well elsewhere. (cimmyt.org)
Grain types, food, and processing
Common grain types include dent, flint, flour, sweet, and popcorn maize. Dent kernels combine hard outer endosperm with a softer central region, whereas flint kernels have a thicker hard layer surrounding a smaller soft center. Flour maize has predominantly soft endosperm. Sweet maize is harvested immature for its higher sugar content; popcorn varieties expand when heated. These categories describe kernel characteristics rather than separate biological species. (fao.org)
Maize supplies carbohydrate, principally starch, together with protein, oil, and dietary fiber. Its composition varies with genotype, growing conditions, and processing. Ordinary maize protein is relatively low in the essential amino acids lysine and tryptophan; quality-protein maize was developed to improve this amino-acid profile. (fao.org)
Nixtamalization involves cooking and steeping grain in an alkaline solution, traditionally containing lime, followed by washing and grinding. It produces the dough used for tortillas and related foods, alters kernel structure, increases calcium content, and improves the availability of niacin. Dry milling produces meal and flour, while wet milling separates starch and other fractions. Fermentation provides another processing route, producing alcoholic beverages and industrial ethanol. (fao.org)
Breeding and genetic research
Commercial hybrid maize is produced by crossing selected parental lines to exploit heterosis, or enhanced performance in the offspring. Seed production must control pollen sources; removing tassels from female parental plants is one method of preventing unwanted self-pollination. Modern breeding also draws on genetic diversity to combine multiple useful traits in locally adapted varieties. (cimmyt.org)
Maize has been a major experimental organism in genetics. Studies of kernel pigmentation and chromosome behavior enabled Barbara McClintock to discover transposable elements, genetic sequences capable of changing position and affecting nearby genes. Her discoveries, made through maize research during the 1940s and 1950s, were recognized with the 1983 Nobel Prize in Physiology or Medicine. (nobelprize.org)
References
- Starch grain and phytolith evidence for early ninth millennium B.P. maize from the Central Balsas River Valley, Mexicopmc.ncbi.nlm.nih.gov
- The cultural and chronological context of early Holocene maize and squash domestication in the Central Balsas River Valley, Mexicopmc.ncbi.nlm.nih.gov
- Maize in human nutrition - Acknowledgments, Preface, Introductionfao.org
- Silk Emergence, Silk Length, and Missing "Butt" Kernelsag.purdue.edu
- Maize in human nutrition - Introduction, Chemical composition and nutritional value of maizefao.org
- The Global Agro-Ecological Zoning version 4: Maize crop profiles3.eu-west-1.amazonaws.com
- Crop yield response to waterfao.org
- CIMMYT releases 32 new elite maize linescimmyt.org
- Maize – CIMMYTcimmyt.org
- Maize in human nutrition - Approaches to improving the nutritive value of maizefao.org