http://www.lanra.uga.edu/peanut/knowledgebase/

Vegetative growth

The peanut Arachis hypogaea is an annual legume, unusual in its genus being polyploid (4x=40). It can interbreed only with another species A. monticola, the probable wild progenitor of the crop . The cultivated peanut plant is an erect or prostrate, usually 15 to 60 cm tall. It is sparsely hairy and, and has a well developed tap root system with many lateral roots. Roots are usually devoid of hairs, and a distinct epidermis. A unique characteristic of the peanut plant is the nyctinastic movements of the leaflets . The leaf blade consists of four oval to obvate leaflets attached to the midrib by small articulations which allow for movement. During dark periods and hot sunny days, the paired leaflets are close together in a vertical position, and on a normal day leaflets are separated from each other in a horizontal position.