Zea

Zea is a genus of grasses in the family Poaceae. Several species are commonly known as teosintes and are found in Mexico, Guatemala, and Nicaragua. There are five recognized species in the genus: Zea diploperennis, Zea perennis, Zea luxurians, Zea … Continue reading

Zea is a genus of grasses in the family Poaceae. Several species are commonly known as teosintes and are found in Mexico, Guatemala, and Nicaragua.

There are five recognized species in the genus: Zea diploperennis, Zea perennis, Zea luxurians, Zea nicaraguensis, and Zea mays. The last species is further divided into four subspecies: huehuetenangensis, mexicana, parviglumis, and mays. The first three subspecies are teosintes; the last is maize, or corn, the only domesticated taxon in the genus Zea. The species are grouped into two sections, sect. Luxuriantes, with the first four species, and sect. Zea with Zea mays. The former section is typified by dark-staining knobs made up of heterochromatin that are terminal on most chromosome arms, while most subspecies of sect. Zea may have 0 to 3 knobs between each chromosome end and the centromere and very few terminal knobs (except Z. m. huehuetenangensis which has many large terminal knobs). The two perennials are thought to be one species by some.

Teosintes are critical components of maize evolution, but opinions vary about which taxa were involved. According to the most widely-held evolutionary model, the crop was derived directly from Z. m. parviglumis by selection of key mutations [3]; up to 12% of its genetic material came from Z. m. mexicana through introgression. Another model proposes that a tiny-eared wild maize was domesticated, and after being spread from east-central Mexico, this cultigen hybridized with Z. luxurians or Z. diploperennis resulting in a great explosion of maize genetic diversity, ear and kernel forms, and capacity to adapt to new habitats, as well as increased yields. A third model suggests that the early maize resulted from a cross between Z. diploperennis and a species of Tripsacum; support for this is minimal. A fourth model posits that teosinte resulted from hybridization between an early wild form of Z. m. mays and Tripsacum.[4]

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, teosintes are regarded by maize farmers as a noxious weed, while in a few areas farmers regard it as a beneficial companion plant, and encourage its introgression into their maize.