The majority of butterworts are perennial plants. All species form stemless rosettes. The thin, white roots serve mainly as an anchor for the plant and to absorb moisture. The leaf blade of a butterworts is smooth, rigid, and succulent, usually bright green or pinkish in colour. The single, long-lasting flowers are zygomorphic, with two lower lip petals characteristic of the bladderwort family, and a spur extending from the back of the flower. The calyx has five sepals, and the petals are arranged in a two-part lower lip and a three-part upper lip. Most butterworts flowers are blue, violet or white, often suffused with a yellow, greenish or reddish tint. The round to egg-shaped seed capsules open when dry into two halves, exposing numerous small, brown seeds. Of the roughly 80 currently known species, 13 are native to Europe, 9 to North America. The largest number of species is in South and Central America. Butterworts are distributed throughout the northern hemisphere.