Zea (plant)
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''Zea'' is a
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...
s in the
grass family Poaceae ( ), also called Gramineae ( ), is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos, the grasses of natural grassland and species cultivated in ...
. The best-known species is ''Z. mays'' (variously called
maize Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...
, 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 that begins in the southern part of North America and extends to the Pacific coast of Central America, thus comprising the lands of central and southern Mexico, all of Belize, Guatemala, El S ...
.


Etymology

''Zea'' is derived from the
Greek Greek may refer to: 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 of all kno ...
name () for another cereal grain (possibly
spelt Spelt (''Triticum spelta''), also known as dinkel wheat is a species of wheat. It is a relict crop, eaten in Central Europe and northern Spain. It is high in protein and may be considered a health food. Spelt was cultivated from the Neolit ...
).Gledhill, David (2008). "The Names of Plants".
Cambridge University Press Cambridge University Press was the university press of the University of Cambridge. Granted a letters patent by King Henry VIII in 1534, it was the oldest university press in the world. Cambridge University Press merged with Cambridge Assessme ...
(CUP). (hardback), (paperback). pp 411


Recognized species

The five accepted
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
names in the
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
are:
Maize Maize (; ''Zea mays''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...
(''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''), also known as corn in North American English, is a tall stout grass that produces cereal grain. It was domesticated by indigenous peoples in southern Mexico about 9,000 years ago from wild teosinte. Native American ...
, or corn, the only domesticated
taxon In biology, a taxon (back-formation from ''taxonomy''; : 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 name and ...
in the genus ''Zea''. The genus is divided into two
sections Section, Sectioning, or Sectioned may refer to: Arts, entertainment and media * Section (music), a complete, but not independent, musical idea * Section (typography), a subdivision, especially of a chapter, in books and documents ** Section sig ...
: ''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 Heterochromatin is a tightly packed form of DNA or '' condensed DNA'', which comes in multiple varieties. These varieties lie on a continuum between the two extremes of constitutive heterochromatin and facultative heterochromatin. Both play a rol ...
that are terminal on most
chromosome A chromosome is a package of DNA containing part or all of the genetic material of an organism. In most chromosomes, the very long thin DNA fibers are coated with nucleosome-forming packaging proteins; in eukaryotic cells, the most import ...
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 fiber ...
and very few terminal knobs (except ''Z. m. huehuetenangensis'', which has many large terminal knobs).


Description

Both annual and
perennial In horticulture, the term perennial ('' per-'' + '' -ennial'', "through the year") is used to differentiate a plant from shorter-lived annuals and biennials. It has thus been defined as a plant that lives more than 2 years. The term is also ...
teosinte species occur. ''Z. diploperennis'' and ''Z. perennis'' are perennial, while all other species are annual. All species are
diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...
(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 two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...
(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 In biology, two closely related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter each other. An initially interbreeding population that splits into two or more distinct spe ...
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 In botany, an inflorescence is a group or cluster of flowers arranged on a plant's stem that is composed of a main branch or a system of branches. An inflorescence is categorized on the basis of the arrangement of flowers on a main axis ( pe ...
. 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 Ruminants are herbivorous grazing or browsing artiodactyls belonging to the suborder Ruminantia that are able to acquire nutrients from plant-based food by Enteric fermentation, fermenting it in a specialized stomach prior to digestion, principa ...
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 flowering plant, angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the sp ...
if treated with a dilute solution of hydrogen peroxide.


Origin of maize and interaction with teosintes

Maize is a grass, related to
sorghum ''Sorghum bicolor'', commonly called sorghum () and also known as great millet, broomcorn, guinea corn, durra, imphee, jowar, or milo, is a species in the Poaceae, grass genus ''Sorghum (genus), Sorghum'' cultivated for its grain. The grain i ...
and more distantly to
rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...
and
wheat Wheat is a group of wild and crop domestication, domesticated Poaceae, grasses of the genus ''Triticum'' (). They are Agriculture, cultivated for their cereal grains, which are staple foods around the world. Well-known Taxonomy of wheat, whe ...
. The genus ''Zea'' is closely related to ''
Tripsacum ''Tripsacum'' is a genus of plants in the Poaceae, grass family and native to the Western Hemisphere. Gamagrass is a common name for plants in this genus. Species References: Formerly included Reference: See ''Anthephora''; ''Apluda''; ''Ch ...
'', gamagrass. Teosintes are critical components of maize domestication, but opinions vary about which
taxa In biology, a taxon (back-formation from ''taxonomy''; : 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 name and ...
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 large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nucleic aci ...
came from ''Z. m. mexicana'' through
introgression Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Introg ...
. All but the
Nicaragua Nicaragua, officially the Republic of Nicaragua, is the geographically largest Sovereign state, country in Central America, comprising . With a population of 7,142,529 as of 2024, it is the third-most populous country in Central America aft ...
n species of teosinte may grow in or very near corn fields, providing opportunities for
introgression Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Introg ...
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, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...
, teosintes are regarded by maize farmers as a noxious
weed A weed is a plant considered undesirable in a particular situation, growing where it conflicts with human preferences, needs, or goals.Harlan, J. R., & deWet, J. M. (1965). Some thoughts about weeds. ''Economic botany'', ''19''(1), 16-24. Pla ...
, 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 weed suppression, pest control, pollination, providing habitat for beneficial insects, maximi ...
, and encourage its
introgression Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Introg ...
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 (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...
e (
caterpillar Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder ...
s) of some
Lepidoptera Lepidoptera ( ) or lepidopterans is an order (biology), order of winged insects which includes butterflies and moths. About 180,000 species of the Lepidoptera have been described, representing 10% of the total described species of living organ ...
n species including (in the Americas) the fall armyworm (''Spodoptera frugiperda''), the corn earworm (''
Helicoverpa zea ''Helicoverpa zea, ''commonly known as the corn earworm, is a species (formerly in the genus ''Heliothis'') in the family Noctuidae. The larva of the moth ''Helicoverpa zea'' is a major agricultural pest (organism), pest. Since it is polyphagous ...
''), and the stem borers '' Diatraea'' and '' Chilo''; in the Old World, it is attacked by the double-striped pug, the cutworms heart and club and
heart and dart The heart and dart (''Agrotis exclamationis'') is a moth of the family Noctuidae. The species was Species description, first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae, 10th edition of ''Systema Naturae''. A familiar m ...
, '' Hypercompe indecisa'', 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 moths, and the European corn borer (''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 is a Latin phrase meaning 'in place' or 'on site', derived from ' ('in') and ' ( ablative of ''situs'', ). The term typically refers to the examination or occurrence of a process within its original context, without relocation. The term is use ...
'' 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.


Genomics

Gene flow In population genetics, gene flow (also known as migration and allele flow) is the transfer of genetic variation, genetic material from one population to another. If the rate of gene flow is high enough, then two populations will have equivalent ...
from genetically modified maize to teosinte weeds has only been observed to produce a GM teosinte with the same trait but this may not always be the outcome. Teosinte with a different insertion of the
transgene A transgene is a gene that has been transferred naturally, or by any of a number of genetic engineering techniques, from one organism to another. The introduction of a transgene, in a process known as transgenesis, has the potential to change the ...
may result and functionally different outcomes may be produced. : : :This review cites this research. :


References


External links

* {{Authority control 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 Andropogoneae