Included in Guttiferae in Michigan Flora. The family is easily recognized by the opposite, entire, punctate leaves (translucent dots ± visible when held to the light, resulting from oil-filled cavities); the inflorescence is cymose, with the terminal flower in each cluster developing first.
1. Petals yellow (occasionally flushed with pinkish), the flowers ordinarily opening; stamens more than 9, or not in distinct groups, without alternating glands; capsules not striate.
1. Petals pink to purple, the flowers rarely open; stamens 9, in 3 distinct groups of 3 each, the groups of basally connate stamens alternating with conspicuous glands; capsules, even when immature, prominently striate longitudinally.