Description: Annual or perennial herbs or subshrubs.
Leaves opposite, rarely whorled.
Flowers solitary or in cymes, sometimes borne in raceme-like conflorescences; zygomorphic, 6-merous. Hypanthium tubular, swollen or spurred on one side at the base; calyx appendages shorter or longer than the lobes. Petals small, usually 6, occasionally absent. Stamens 11, rarely 9 or 6, included to exserted, 2 inserted lower in the hypanthium than the other 9. Ovary incompletely 2-locular; style slender, included to exserted.
Capsule enclosed in the hypanthium, the whole structure splitting down one side; seeds numerous to few.
Distribution and occurrence: World: c. 250 species, tropical America. Australia: 1 species (naturalized).
Text by J. Highet & Peter G. Wilson
Taxa not yet included in identification key