Home Page

Research

Teaching

Publications

Lab Members

Data Files

Images

Contact Us

Links

The Taxonomy of Zea
John Doebley
Laboratory of Genetics
University of Wisconsin-Madison
© John Doebley 2003
 

The genus Zea is a member of the grass family (Poaceae) and composed of four species native to Mexico and Central America. The base chromosome number for Zea is x=10. Zea includes maize or Indian corn as well as the teosintes, the closest wild relatives of maize. The name teosinte comes from Náhuatl language of Mexico and it has been suggested that its meaning is maize (centli) of the gods (teo) (Wilkes 1967). Teosinte is the common name that applies to four botanical species. On this web page, I briefly summarize the taxonomic system for Zea that Hugh Iltis and I proposed while I was his graduate student (Doebley and Iltis 1980; Iltis and Doebley 1980). I also provide a brief description of Zea's sister genus, Tripsacum.

The taxonomy presented here was developed as a guide for field biologists. Thus, the emphasis is on groups that can be distinguished based on visible, morphological traits, especially traits that are preserved on herbarium specimens.

1. Zea diploperennis Iltis, Doebley and Guzman

This species, as its name signifies, is a diploid (n=10) perennial. It has a very narrow geographic distribution, being found only in a small region of the Sierra de Manantlán in the southwestern part of the state of Jalisco, Mexico at altitudes of 1400-2400 m (see map). The plants in their native habitat are typically ~2 to 2.5 m tall. The defining morphological features of this species are (1) tassels with relatively 2-15, somewhat lax, branches, (2) fruitcases that are trapezoidal in outline, and (3) both long, slender, cord-like rhizomes and thick, short, tuberous rhizomes (see photos). English common name: diploperennial teosinte.

2. Zea perennis (Hitchcock) Reeves and Mangelsdorf

This species is a tetraploid (n=2x=20) perennial. It is the only polyploid in the genus. It has a narrow geographic distribution on the northern slopes of Volcán de Colima in the state of Jalisco at altitudes of 1500-2000 m (see map). The plants in their native habitat are typically ~1.5 to 2 m tall. Zea perennis is quite similar to Z. diploperennis, but it can be distinguished from Z. diploperennis by several features: (1) tetraploidy, (2) presence of slender, elongated rhizomes but not thick, short rhizomes, and (3) 2-8 erect tassel branches (see photos). English common name: perennial teosinte.

3. Zea luxurians (Durieu and Ascherson) Bird*

This species is an annual native to southeastern Guatemala, Honduras and Nicaragua at altitudes between sea level and 1100 m (see map). It is also known from a single collection made in Oaxaca, Mexico in 1845, although no one has recollected it from this locality since that time. Z. luxurians is an annual and lacks rhizomes, yet it has some features in common with the two perennial species. Its tassels have relatively few (~4-20) erect branches, and its fruitcases are trapezoidal in outline. The outer glumes of its male spikelets have numerous fine veins that distinguish it from other Zea species (see photos), but resemble the glumes of the sister genus, Tripsacum. The plants in their native habitat are typically ~3 to 4 m tall. English common name: Guatemala or Florida teosinte.

4. Zea mays Linnaeus

This is the species to which maize itself belongs. Hugh Iltis and I also placed some annual teosintes into Z. mays to emphasize their close biological relationship to maize (Iltis and Doebley 1980). We applied the biological species concept to Zea. Since maize and these teosintes are easily cross hybridized and their hybrids are fully fertile, they belong in the same biological species despite the fact that maize and these teosintes look remarkably different (see The Morphology of Maize and Teosinte). We have defined four subspecies including three types of teosinte and maize. In the descriptions below, I emphasize the traits that distinguish the three teosinte subspecies from one another.

4a. Zea mays L. ssp. huehuetenangensis (Iltis and Doebley) Doebley

This is a form of teosinte found in western Guatemala at elevations of 900-1650 m above sea level (see map). It is distinguished from the other teosinte subspecies of Z. mays by its longer life cycle, taking 7-8 months from germination to seed maturation in its native habitat. As a consequence, the plants are much taller than most other teosintes (up to 5 m). Its floral morphology is so similar to ssp. parviglumis (below) that Hugh Iltis and I found no traits by which we could distinguish these two taxa on the basis of their tassel and ear morphology (Iltis and Doebley 1980; Doebley 1983; Doebley 1990). Both ssp. huehuetenangensis and parviglumis have many tassel branches (20 or more) in vigorous plants, and their fruitcases (~30-60 mg) and tassel spikelets (5-7 mm long) are relatively small. The fruitcase are ± triangular in outline. English common name: Huehuetenango teosinte.

4b. Zea mays L. ssp. mexicana (Schrader) Iltis

This subspecies is found at altitudes from about 1700 to 2600 m in central and northern Mexico. It ranges from Puebla to the Nobogame Valley in Chihuahua (see map). At these relatively high elevations and northern localities, this subspecies has a rapid life cycle with plants taking only 4-6 months from germination to seed maturation depending on the specific population. In a growth chamber, some forms of this subspecies can mature their seeds in under 75 days. Plant height ranges from ~1.5 to 4 m along a north-south cline. Subspecies mexicana typically has 10-20 tassel branches, but I have seen exceptional plants with up to 35 (see photos). Its fruitcases (~60-95 mg) and tassel spikelets (6-10 mm long) are relatively large, and these features help to distinguish it from ssp. parviglumis and huehuetenangensis. The fruitcases are triangular in outline.

Populations of this subspecies in the Valley of Mexico (Race Chalco) at elevations above 2000 m commonly have dark red, hairy leaf sheaths. Populations throughout the Mesa Central (Race Central Plateau) typically have green to weak red, glabrous to sparsely hairy leaf sheaths. The northern most population in the Nobogame Valley of Chihuahua (Race Nobogame) is the shortest and earliest flowering teosinte. English common name: Mexican annual teosinte.

4c. Zea mays L. ssp. parviglumis Iltis and Doebley

This subspecies is found at elevations between about 400 and 1800 m above sea level in the valleys along the western escarpment of Mexico from Nayarit to Oaxaca (see map). At lower, warmer elevations than ssp. mexicana, it takes about 6-7 months to mature its seed. Plant height ranges from ~2 to nearly 5 m. The plants typically have green to weak red, glabrous leaf sheaths. The name "parviglumis" means small glume, referring to the small (5-8 mm) tassel spikelets. It has similarly small fruitcases (~30-80 mg). This subspecies is also typified by a large number of tassel branches, usually more than 20 and exceeding 100 in the most robust plants (see photos). The fruitcases are ± triangular in outline.

Populations are distributed along and east-west axis from Oaxaca to Jalisco. Populations in the center of this range in the Balsas river drainage are known as Race Balsas or Balsas teosinte. English common name: Mexican annual teosinte.

4d. Zea mays L. ssp. mays

The final subspecies is maize. Maize differs so radically in plant and ear morphology from the three teosinte subspecies of Z. mays that I have devoted a separate web page to describe these differences (The Morphology of Maize and Teosinte). Hugh Iltis and I connected maize and these three teosinte subspecies together in Z. mays largely because of the similarity in the structure of their tassels. For example, the glumes of the tassel spikelets of maize and these three teosintes all have relatively few widely-spaced veins (photos) as compared to Z. diploperennis, Z. perennis and Z. luxurians. There are other (non-morphological) features that bind maize and sspp. huehuetenangensis, parviglumis and mexicana together that I describe separately (The Phylogeny of Zea).

Sectional Division of Zea: When Hugh Iltis and I conducted our taxonomic division of Zea, the genus was divided into two sections: section Euchlaena (the original genus name for teosinte), which included all the teosintes, and section Zea, which included only maize. We felt this division was inappropriate since it placed the emphasis on the aspects of morphology that were the results of recent human selection during maize domestication (Doebley and Iltis 1980). Our desire was to place the emphasis on the deeper phylogenetic divisions that distinguish the different forms of teosinte, even though these are reflected by only modest morphological differences as compared to the radical morphological differences between maize and teosinte. We divided the four species into section Luxuriantes and section Zea.

Section Luxuriantes contains Z. diploperennis, Z. perennis and Z. luxurians. This is the more "primitive" of the sections in that, for many morphological traits, the species of this section more closely resemble plants of the sister genus Tripsacum than does the single species of section Zea. This closer resemblance includes features such as the perennial habit (presence of underground rhizomes), thicker inflorescence branches, shorter pedicels in the male spikelets, and fruitcases that are trapezoidal in outline.

Section Zea contains only Z. mays with its four subspecies. The species are all annual, have more slender tassel branches (although secondarily thickened in cultivated maize), and have longer pedicels in the male spikelets as compared to plants of section Luxuriantes. The teosintes that belong to section Zea all have fruitcases that are ± triangular in outline.

Other Zea taxonomies: Taxonomic classifications are not chiseled in stone and other researchers have treated Zea differently from the taxonomic system outlined above. For example, Wilkes (1967) recognized Z. perennis, but places Z. luxurians, Z. mays ssp. mexicana, ssp. parviglumis, and ssp. huehuetenangensis together in the single species, Z. mexicana. He considered maize (Z. mays) as a species separate from all teosintes (Z. perennis and Z. mexicana). His taxonomy places the emphasis on morphology — because maize and teosinte look so different he keeps them in separate species (Z. mays and Z. mexicana). As noted above, Hugh Iltis and I have put the emphasis on the biological species concept, placing some teosintes and maize into the same species because of their cross compatibility and the fertility of their hybrids. We further de-emphasize traits that have changed as a result of recent human selection.

The genus Tripsacum: The genus Tripsacum is the most closely related genus to Zea. For this reason, it has held a prominent place in Zea research. Tripsacum is a New World native with 13 recognized species that range from Massachusetts to Paraguay. The base chromosome number is x=18 and there are diploid, triploid, tetraploid and higher ploidy levels in the genus. Natural hybrids between species are common resulting in intermediate forms that obscure species boundaries. One "Tripsacum" species (T. andersonii) is actually a sterile Zea-Tripsacum hybrid. All members of the genus are perennials. They are robust grasses, ranging from 1 to 5 m. Two easily discerned morphological features distinguish Tripsacum species from Zea species. First, Tripsacum inflorescence branches have distal male spikelets and basal female spikelets (photos) unlike Zea in which there are separate male and female inflorescences (although teosinte, and more rarely maize, do form some mixed inflorescences). Second, their fruitcases are less indurate, more cylindrical in cross section, and rectangular-trapezoidal in outline. I know of no recent review of the genus except for the one I wrote myself (Doebley 1983b), which is published in an obscure conference proceeding, but if you send me an email, I have a few copies left and I'll send you one.

Annotated Bibliography:

Taxonomy is a dynamic enterprise with more recent authors constantly modifying and redefining the nomenclatures and classifications of earlier workers. As a consequence, reading a paper on teosinte written in the 1930s can be confusing in that the familiar species and subspecies names of the present are either not used or used with a different meaning. Bear this in mind when reading this literature and refer to Iltis and Doebley (1980) for a guide to the nomenclature.

  1. Collins, G. N., 1921. Teosinte in Mexico. J. Heredity 12:339-350. [An early and influential paper that helped promote research on teosinte.]
  2. Doebley, J., 1983. The maize and teosinte male inflorescence: a numerical taxonomic study. Ann. Missouri Bot. Gard. 70:32-70. [This paper gives detailed descriptions of the male inflorescences of the species along with accompanying photographs.]
  3. Doebley, J., 1983. The taxonomy and evolution of Tripsacum and teosinte, the closest relatives of maize. Pp. 15-28 in D. T. Gordon, J. K. Knoke and L. R. Nault, eds., Proc. Intl. Maize Virus Disease Colloquium and Workshop. The Ohio State University, Ohio Agricultural Research and Development Center, Wooster, Ohio. [This paper gives brief descriptions of the species of Zea and Tripsacum including some illustrations and distribution maps for the species.]
  4. Doebley, J., 1990. Molecular systematics of Zea (Gramineae). Maydica 35:143-150. [This is a short review in which I elevated Huehuetenango teosinte to a subspecies.]
  5. Doebley, J., and H. H. Iltis. 1980. Taxonomy of Zea (Gramineae). I. A subgeneric classification with key to taxa. Amer. J. Bot. 67:982-993. [This paper and the one below present the taxonomic system for Zea discussed above. It also provides a key to the species.]
  6. Iltis, H. H., and J. F. Doebley. 1980. Taxonomy of Zea (Gramineae). II. Subspecific categories in the Zea mays complex and a generic synopsis. Amer. J. Bot. 67:994-1004.
  7. Sanchez G., J. J., T. A. Kato, M. Aguilar, J. M. Hernandez, A. Lopez and J. A. Ruiz, 1998. Distribucion y caracterizacion del teocintle. Instituto Nacional de Investigciones Forestales, Agricolas y Pecuarias, Guadalajara. [This work and the one below by Sanchez and Ordaz are the two most recent and thorough publications on teosinte. They describe many new populations, major range extensions, and present extensive data on teosinte in Mexico.]
  8. Sanchez G., J., and L. Ordaz S. 1987. El teosinte in Mexico: distribucion actual de las poblaciones. International Board for Plant Genetic Resources, Systematic and Ecogeographic Studies on Crop Genepools No. 2.

* Iltis and Benz (2000, Novon 10: 382-390) have treated populations of this species from Nicaragua as a separate species - Zea nicaraguensis.

 

Home

Top of Page

  Last updated January 14, 2005