Mostly perennial (rarely biennial) herbs or shrubs, with erect or straggling stems from a fibrous or woody rootstock. Leaves paired or in whorls of 3–5; stipules divided into 2-many filiform colleter-tipped segments. Flowers small to very large, hermaphrodite, mono-, di- or tri-morphic, mostly in much-branched terminal complicated cymose inflorescences, the individual branches often becoming spicate in fruit. Calyx-tube ovoid or globose, sometimes with a free annular part at the top; lobes usually 5, either equal or unequal, 1–3 being larger than the others or sometimes foliaceous. Corolla-tube shortly cylindrical to narrowly tubular, 2–40 times as long as wide, hairy in the throat; lobes ovate or oblong. In monomorphic flowers stamens enclosed in an abrupt apical dilation of the tube and style exserted; in dimorphic flowers the tube is gradually dilated at the apex in short-styled flowers and abruptly dilated in long-styled flowers; in rare cases, trimorphism is shown and the third form has both stamens and style included in the tube. Ovary bilocular, with numerous ovules in each attached to placentas affixed to the septum. Capsule obtriangular or ovoid, ribbed, beaked, opening at the apex, the beak splitting into 4 valves; capsule sometimes separating into 2 cocci. Seeds minute, brownish, irregularly globose or tetrahedral, with reticulate testa. Rhaphides are plentiful in most of the tissues.