Herbs, shrubs, or trees. Leaves opposite, usually connected by interpetiolar stipules or by a raised line, simple, entire or toothed. Flowers regular, hermaphrodite or unisexual by abortion. Calyx inferior, 4–5-lobed or -partite; lobes valvate or imbricate or contorted. Stamens 4–5, inserted on the tube of the corolla and alternate with its lobes; anthers 2-celled, with longitudinal dehiscence. Ovary superior, 2-celled or rarely 3–5-celled; style simple; stigma capitate or 2-lobed; ovules 1 or more in each cell. Fruit a 2-celled capsule with septicidal dehiscence or an indehiscent berry. Seeds 1 or more to each cell; albumen copious; embryo straight, long or short.

Distribution chiefly tropical and subtropical, with a few species in temperate North America and in the south temperate zone. Genera 30; species about 350. The order must be considered.a dangerous one, including a large proportion of highly poisonous plants. Strychnine is obtained from the seed of Strychnos nux-vomica, a common Indian tree; and a substance called curare, derived from the bark of two species of Strychnos, is used by the South American Indians to poison their arrows.

Herbs. Flowers 4-merous. Corolla-lobes valvate. Capsule didymous, truncate or 2-lobed	1. Mitrasacme
Herbs or shrubs. Flowers 5-merous. Corolla-lobes imbricate. Capsule ovoid or oblong	2. Logania.
Shrubs. Flowers 5-merous. Corolla-lobes contorted. Placentas forming a pulpy mass enclosing the seeds	3. Geniostoma.