''Zea'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
s in the
grass family. The best-known species is ''Z. mays'' (variously called
maize
Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...
, corn, or Indian corn), one of the most important crops for human societies throughout much of the world. The four wild species are commonly known as teosintes and are native to
Mesoamerica
Mesoamerica is a historical region and cultural area in southern North America and most of Central America. It extends from approximately central Mexico through Belize, Guatemala, El Salvador, Honduras, Nicaragua, and northern Costa Rica ...
.
Etymology
''Zea'' is derived from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
name () for another cereal grain (possibly
spelt).
[Gledhill, David (2008). "The Names of Plants". Cambridge University Press. (hardback), (paperback). pp 411]
Recognized species
The five accepted
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
names in the
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
are:
''
Zea mays'' is further divided into four subspecies: ''Z. m. huehuetenangensis'', ''Z. m. mexicana'', ''
Z. m. parviglumis'' (Balsas teosinte, the ancestor of maize), and ''Z. m. mays''. The first three subspecies are teosintes; the last is
maize
Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...
, or corn,
the only domesticated
taxon
In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...
in the genus ''Zea''.
The genus is divided into two
sections: ''Luxuriantes'', with ''Z. diploperennis'', ''Z. luxurians'', ''Z. nicaraguensis'', ''Z. perennis''; and ''Zea'' with ''Z. mays''. The former section is typified by dark-staining knobs made up of
heterochromatin that are terminal on most
chromosome
A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
arms, while most subspecies of section ''Zea'' may have none to three knobs between each chromosome end and the
centromere
The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers ...
and very few terminal knobs (except ''Z. m. huehuetenangensis'', which has many large terminal knobs).
Description
Both
annual
Annual may refer to:
*Annual publication, periodical publications appearing regularly once per year
** Yearbook
** Literary annual
*Annual plant
*Annual report
*Annual giving
*Annual, Morocco, a settlement in northeastern Morocco
*Annuals (band), ...
and
perennial
A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wid ...
teosinte species occur. ''Z. diploperennis'' and ''Z. perennis'' are perennial, while all other species are annual. All species are
diploid (n=10) with the exception of ''Z. perennis'', which is
tetraploid
Polyploidy is a condition in which the cells of an organism have more than one pair of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contains ...
(n=20). The different species and subspecies of teosinte can be readily distinguished based on morphological, cytogenetic, protein, and DNA differences and on geographic origin. The two perennials are
sympatric and very similar and some consider them to be one species. What many consider to be the most puzzling teosinte is ''Z. m. huehuetenangensis'', which combines a morphology rather like ''Z. m. parviglumis'' with many terminal chromosome knobs and an isozyme position between the two sections. Considered to be phenotypically the most distinctive, as well as the most threatened, teosinte is ''Zea nicaraguensis''. This teosinte thrives in flooded conditions along 200 m of a coastal estuarine river in northwest Nicaragua.
Teosintes strongly resemble maize in many ways, notably their tassel (male inflorescence) morphology. Teosintes are distinguished from maize most obviously by their numerous branches each bearing bunches of distinctive, small female
inflorescences
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed ...
. These spikes mature to form a two-ranked 'ear' of five to 10 triangular or trapezoidal, black or brown disarticulating segments, each with one seed. Each seed is enclosed by a very hard fruitcase, consisting of a cupule or depression in the rachis and a tough lower glume. This protects them from the digestive processes of
ruminants that forage on teosinte and aid in seed distribution through their droppings. Teosinte seed exhibits some resistance to germination, but will quickly
germinate
Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fer ...
if treated with a dilute solution of hydrogen peroxide.
Origin of maize and interaction with teosintes
Teosintes are critical components of
maize
Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. The ...
evolution
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
, but opinions vary about which
taxa
In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...
were involved. According to the most widely held evolutionary model, the crop was derived directly from ''Z. m. parviglumis'' by selection of key mutations;
but in some varieties up to 20% of its
genetic material
Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main clas ...
came from ''Z. m. mexicana'' through
introgression.
All but the
Nicaraguan species of teosinte may grow in or very near corn fields, providing opportunities for
introgression between teosinte and maize. First, and later-generation hybrids are often found in the fields, but the rate of gene exchange is quite low. Some populations of ''Z. m. mexicana'' display
Vavilovian mimicry within cultivated maize fields, having evolved a maize-like form as a result of the farmers' selective weeding pressure. In some areas of
Mexico
Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
, teosintes are regarded by maize farmers as a noxious
weed
A weed is a plant considered undesirable in a particular situation, "a plant in the wrong place", or a plant growing where it is not wanted.Harlan, J. R., & deWet, J. M. (1965). Some thoughts about weeds. ''Economic botany'', ''19''(1), 16-24. ...
, while in a few areas, farmers regard it as a beneficial
companion plant
Companion planting in gardening and agriculture is the planting of different crops in proximity for any of a number of different reasons, including pest control, pollination, providing habitat for beneficial insects, maximizing use of space, and ...
, and encourage its
introgression into their maize.
Early dispersal of maize in the Americas
According to Matsuoka et al., the available early maize gene pool can be divided into three clusters:
* An Andean group, that includes the hand-grenade-shaped ear types and some other Andean maize (35 plants);
* All other South American and Mexican maize (80 plants);
* U.S. maize (40 plants)
Also, some other intermediate genomes, or admixtures of these clusters occur.
According to these authors, "The maize of the Andes Mountains with its distinctive hand grenade-shaped ears was derived from the maize of lowland South America, which in turn came from maize of the lowlands of Guatemala and southern Mexico."
Ecology
''Zea'' species are used as food plants by the
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
...
e (
caterpillars) of some
Lepidoptera species including (in the Americas) the
fall armyworm (''Spodoptera frugiperda''), the
corn earworm (''Helicoverpa zea''), and the stem borers ''
Diatraea'' and ''
Chilo''; in the Old World, it is attacked by the
double-striped pug, the
cutworm
Cutworms are moth larvae that hide under litter or soil during the day, coming out in the dark to feed on plants. A larva typically attacks the first part of the plant it encounters, namely the stem, often of a seedling, and consequently cuts it ...
s
heart and club and
heart and dart
The heart and dart (''Agrotis exclamationis'') is a moth of the family Noctuidae. The species was first described by Carl Linnaeus in his 1758 10th edition of ''Systema Naturae''. A familiar moth to many, it is considered one of the most commo ...
, ''
Hypercompe indecisa
''Hypercompe indecisa'' is a moth of the family Erebidae first described by Francis Walker in 1855. It is found in Argentina and Uruguay.
Larvae have been recorded feeding on ''Beta'', ''Brassica'', ''Citrus'', ''Cucurbita'', ''Datura'', ''Dio ...
'', the
rustic shoulder-knot, the
setaceous Hebrew character
The setaceous Hebrew character (''Xestia c-nigrum'') is a moth of the family Noctuidae. The species was first described by Carl Linnaeus in his 1758 10th edition of ''Systema Naturae''. It is found in the Palearctic realm. It is a common specie ...
and
turnip moth
''Agrotis segetum'', sometimes known as the turnip moth, is a moth of the family Noctuidae. The species was first described by Michael Denis and Ignaz Schiffermüller in 1775. It is a common European species and it is found in Africa and across ...
s, and the
European corn borer
The European corn borer (''Ostrinia nubilalis''), also known as the European corn worm or European high-flyer, is a moth of the family Crambidae which includes other grass moths. It is a pest of grain, particularly maize (''Zea mays''). The in ...
(''Ostrinia nubilalis''), among many others.
Virtually all populations of teosintes are either threatened or endangered: ''Z. diploperennis'' exists in an area of only a few square miles; ''Z. nicaraguensis'' survives as about 6000 plants in an area of 200 × 150 m. The Mexican and Nicaraguan governments have taken action in recent years to protect wild teosinte populations, using both ''
in situ
''In situ'' (; often not italicized in English) is a Latin phrase that translates literally to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in ...
'' and ''
ex situ'' conservation methods. Currently, a large amount of scientific interest exists in conferring beneficial teosinte traits, such as nitrogen fixation,
insect resistance, perennialism, and flood tolerance, to cultivated maize lines, although this is very difficult due to linked deleterious teosinte traits.
References
External links
*
{{Taxonbar, from=Q542456
Grasses of North America
Grasses of South America
Agriculture in Mesoamerica
Crops originating from North America
Crops originating from South America
Crops originating from Pre-Columbian North America
Zea
Taxa named by Carl Linnaeus