What type of plant do peanuts come from

A peanut plant is an annual plant that grows to about 18 inches high . The peanut forms like a legume on the plant and then goes like a mole under the earth to mature into its adult form

This is a good site for information about peanuts:
http://peanutvan.com.au/growing.htm

Peanuts are legumes with a very unique growth cycle. There are four principal varieties under commercial cultivation around the world: Virginia, Runner, Spanish and Valencia.
Virginia and Runner peanuts are low, bushy plants which have two large seeds per pod. Spanish and Valencia are more erect and have smaller seeds. Each different variety is suited to certain soils and climatic conditions - and today, Australian agricultural scientists are developing a wide range of sub-types of these four basic variants to extend the plants further.
In the USA, peanuts are also widely known as goobers, goober peas, groundpeas, ground nuts or earth nuts. Here in Australia, though, we generally call them peanuts wherever they're grown and regardless of the variety being cultivated.

They grow on the roots of peanut plants,peanuts also act as a good plant for adding nitrogen to the soil,plants that do this are called legumeus plants,there are heaps of peanut plants here,here is a few pictures and link-http://en.wikipedia.org/wiki/Peanut

They grow best in sandy soil, (because the peanut is underground, still in its shell), with a leafy top above ground. They used to grow a lot of peanuts up along the Red River in Texas.

Legumes. The following is from wikipedia

The peanut, or groundnut (Arachis hypogaea) is a species in the legume family Fabaceae native to South America. It is an annual herbaceous plant growing to 30 to 50 cm (1 to 1½ feet) tall. The leaves are opposite, pinnate with four leaflets (two opposite pairs; no terminal leaflet), each leaflet 1 to 7 cm (⅜ to 2¾ in) long and 1 to 3 cm (⅜ to 1 inch) broad. The flowers are a typical peaflower in shape, 2 to 4 cm (¾ to 1½ in) across, yellow with reddish veining. After pollination, the fruit develops into a legume 3 to 7 cm (1 to 2 in) long containing 1 to 4 (rarely 5) seeds, which forces its way underground to mature.

Although a nut in the culinary sense, in the botanical sense the fruit of the peanut is a woody, indehiscent legume or pod and not a nut.

"The peanut plant (Arachis hypogea) is a legume that is native to South America (it now grows in warm areas around the world).

The peanut plant grows to about about 60 cm tall. It has small yellow flowers (1-2 cm long). The flowers bloom for only about half a day; the blossoms are self-pollinating. About 4 days later, a stem (also called a peg) will grow from the flower and head into the soil. At the end of each stem, the seed pods (peanuts in the shell) will grow. The peanut is an annual plant (it completes its life cycle in one year)."

Source:http://www.enchantedlearning.com/subjects/plants/pages/peanutplant.shtml