Potato is one of some 150 tuber-bearing species of the genus Solanum (a tuber is the swollen end of an underground stem). The compound leaves are spirally arranged; each leaf is 20–30 cm (about 8–12 inches) long and consists of a terminal leaflet and two to four pairs of leaflets. The white, lavender, or purple flowers have five fused petals and yellow stamens. The fruit is a small poisonous berry with numerous seeds.