A large family, widely distributed, most abundant in temperate regions; smooth herbs, with colorless, bitter juice; leaves toothless, usually opposite, without leafstalks or stipules; flowers regular; calyx four to twelve-toothed; corolla with united lobes, twisted or overlapping in the bud, of the same number as the calyx-teeth; stamens inserted on the tube or throat of the corolla, as many as its lobes, alternate with them; ovary superior, mostly one-celled, with a single style or none, and one or two stigmas; fruit a capsule, mostly with two valves, containing many seeds. These plants were named for King Gentius of Illyria, said to have discovered their medicinal value.

There are several kinds of Frasera, North American, all but one western; herbs, with thick, bitter, woody roots; leaves opposite or in whorls; flowers numerous; corolla wheel-shaped, with four divisions, each with one or two fringed glands and sometimes also a fringed crown at base; stamens on the base of the corolla, with oblong, swinging anthers, the filaments often united at base; ovary egg-shaped, tapering to a slender style, with a small, more or less two-lobed, stigma; capsule leathery, egg-shaped, with flattish seeds.