Zea Mays (Maize, Corn)


Zea mays L. (maize, corn) is a member of the grass family (Poaceae). It has been an important food crop since ancient times, especially among the peoples of Central and South America. Although most grasses have bisexual florets the mature florets of Z. mays are functionally unisexual on the sample plant, a condition referred to as monoecy. The functionally male florets are borne on the tassel whereas the functionally female florets are borne on the ear. All of the components of the adult Z. mays plant are initiated within the first 4 weeks after germination. Research on maize genetics has led to some exciting discoveries (some associated with the award of a Nobel prize). These discoveries have clarified the putative origin and biology of Z. mays and have also provided significant insights for plant biology as a whole. An overview of the taxonomy of Z. mays is provided.

Key Concepts:

  • The species, Zea mays L. (maize/corn), is a member of the grass family (Poaceae) and a member of the genus Zea. Taxonomically and nomenclaturally maize is known as Z. mays L. ssp. mays.

  • Maize is considered to have evolved from the Mexican annual teosintes (Z. mays ssp. parviglumis and ssp. mexicana).

  • A large number of exciting genetic discoveries originated from the research on maize. One of these discoveries, the phenomenon of transposable elements, resulted in the awarding of a Nobel prize.

  • The flowers of Z. mays, typically referred to as florets, are initially bisexual but before the florets are reproductively functional they become unisexual, resulting in monoecy.

  • The functionally male florets are borne terminally on the plant in the tassel. The functionally female florets are borne laterally on the plant in one or more ears.

  • The occurrence of separate male and female florets in separate flowering structures (inflorescences) on the Z. mays plant (monoecy) has enabled the genetics of this species to be extensively studied because controlled pollinations are relatively easily performed.

  • The morphological structure of the very young florets in Z. mays is typical of the florets in the grass family (Poaceae) in that each floret is subtended by a lemma and a palea. Pairs of florets form spikelets.

  • In the tassel, both florets in each spikelet are functionally male and produce pollen. In the ear one of the two florets in each spikelet aborts. The remaining floret results in a kernel following successful pollination and fertilisation.

Keywords: corn; grass; maize; Poaceae; Zea mays; monoecy; transposons; C4 photosynthesis; cold sensitivity

Figure 1.

A photo of a whole plant of Zea mays grown in Columbia, Missouri, USA (2000). Note that most of the root system has been removed. The background is of a field of maize/corn plants at a research farm.

Figure 2.

Various images of teosinte and maize. Maize is considered to have evolved from the Mexican annual teosintes (Z. mays ssp. parviglumis and ssp. mexicana) (clockwise from top left): Ears of Z. mays ssp. parviglumis and maize (photo: Hugh Iltis); Teosinte ear (Z. mays ssp. mexicana) on the left, maize ear on the right, and ear of their F1 hybrid in the centre (photo: John Doebley); Teosinte and ‘reconstructed’ primitive maize. George Beadle created the latter by crossing teosinte with Argentine pop corn and then selecting the smallest segregants. This ‘reconstructed’ maize ear resembles the earliest archaeological corn recovered from the tehuacán valley in Mexico (photo: John Doebley); Z. mays ssp. mexicana Race Chalco plant (photo: Hugh Iltis); Immature ears of Z. mays ssp. parviglumis (photo: Hugh Iltis); A sample of the diversity represented in the corn crib of one farmer in the highlands of central Mexico. The corn shown is of the Mexican Pyramidal Complex, named for the conical or ‘pyramid’ shaped ears (photo: Hugh Iltis). All images gratefully provided by John Doebley (teosinte.wisc.edu/images.html).

Figure 3.

Diagrammatic representation of a pair of tassel (male) spikelets (a) and a pair of ear (female) spikelets (b). (Graphic art by Stephanie Moore.) P, palea; L, lemma; LG, lower glume; UG, upper glume; F1, more mature upper floret; F2, less mature lower floret; PS, pedicellate spikelet; SS, sessile spikelet; I, portion (of rachis or lateral branch) of tassel (male) inflorescence; AF, aborted floret; F, functional female floret of ear; C, portion of cob (thick central axis of the female flowering system); Pe, pedicel.

Figure 4.

The mature kernel: 1 and 2 are vertical sections in two planes of a mature kernel (‘seed’) of dent corn, showing detailed arrangement of organs and tissues. a, Silk scar; b, pericarp; c, aleurone; d, endosperm; e, scutellum; f, glandular layer of scutellum; g, coleoptile; h, plumule with stem and leaves; i, first internode; j, adventitious lateral root; k, scutellar node; l, primary root; m, coleorhiza; n, basal conducting cells of endosperm; o, brown abscission layer; p, pedicel or flower stalk. (Reproduced with permission from Kiesselbach TA (1949) The Structure and Reproduction of Corn. Nebraska Agricultural Experimental Station. Annual Report 161: 1–96. Reprinted 1999, available from Cold Spring Harbor Laboratory Press.)

Figure 5.

A young corn seedling showing early stages in the development of various types of roots and the early stage of leaf development. (Reproduced with permission from Freeling and Walbot .)

Figure 6.

Maize reproduction. (a) Pistil (female reproductive organs) of maize. The pistil is shown at the time at which the pollen tube (male gametophyte) enters the embryo sac (female gametophyte). The stigma – the sticky surface of the flower that receives the pollen – and the style – the stalk connecting the stigma to the ovary – are shown. (b) Double fertilisation: Double fertilisation describes the plant‐specific process by which two sperm from the pollen tube enter the embryo sac (A); one fertilises the egg, which leads to the embryo proper, whereas the other fertilises one of the two polar nuclei (B), before fusing with the second polar nucleus to form the triploid endosperm that will nourish the embryo (C). (Reproduced with permission from Macmillan Publishers Ltd: www.nature.com/reviews/genetics doi:10.1038/35098524.) Copyright by Nature Publishing Group.



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Further Reading

Chapman GP (1996) The Biology of Grasses. New York: CAB International.

Interactive Maize Plant (IMP) (http://www.maizegdb.org/IMP/)

Kiesselbach TA (1999) The Structure and Reproduction of Corn (50th Anniversary Edition). Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press.

Sheridan WF (ed.) (1982) Maize for Biological Research. Charlottesville, VA: Plant Molecular Biology Association.

Sprague GF (ed.) (1955) Corn and Corn Improvement, Agronomy 5. New York: Academic Press.

Web Links

Maize Genetics and Genomics Database (MaizeGDB) (www.maizegdb.org)

University of Missouri‐Columbia. Interactive Maize Plant (IMP) (http://www.agron.missouri.edu/IMP/frames_imp2.html)

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Vincent, P Leszek D(Aug 2012) Zea Mays (Maize, Corn). In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003687.pub2]