Nearly all of the Bignoniaceae are woody plants, but a few are subwoody, either as vines or subshrubs. A few more are herbaceous plants of high-elevation montane habitats. The family has a nearly cosmopolitan distribution, but is mostly tropical, with a few species native to the temperate zones. Its greatest diversity is in northern South America. Bignoniaceae are most noted for ornamentals, such as Jacaranda, Tabebuia, and Spathodea, grown for their conspicuous, tubular flowers.
The leaves are petiolate. Leaf arrangement usually is opposite, or rarely alternate or verticillate (in whorls). Leaves are usually compound, bifoliate, trifoliate, pinnate, or palmate, or rarely simple. Stipules are absent but persistent; enlarged axillary bud scales (pseudostipules) are often present. Domatia occur in some genera.
Flowers are solitary or in inflorescences in a raceme or a helicoid or dichasial cyme. Inflorescences bear persistent or deciduous bracts or bractlets. The flowers are hypogynous, zygomorphic, bisexual, and usually conspicuous. The calyx and corolla are distinct. The calyx is synsepalous, with five sepals. The corolla is sympetalous, with five petals, often bilabiate. Corolla lobes are imbricate in bud, or rarely valvate, and usually much shorter than the corolla tube. Stamens are inserted on the corolla tube, alternating with corolla lobes. The four stamens are didynamous, members of each pair often connivent, the adaxial stamen is usually staminodial or absent; rarely with five fertile stamens or with two fertile and three staminodial stamens. The stigma is bilobed, and usually sensitive; a style is present. The ovary is superior, usually surrounded by a nectary disk, composed of two carpels, bilocular and with a septum, except unilocular in Tourrettia and quadrilocular in Eccremocarpus. Placentation is axile, except parietal in Tourrettia. Ovules are numerous.
The fruit is usually a bivalved capsule, often with a replum. Dehiscence is septicidal or loculicidal. The three exceptions are the genera Kigelia, Crescentia and its close relatives, and Colea and its close relatives. In these, the fruit is indehiscent, not a capsule, and the seeds are not winged. The fruit is a berry in Colea. Seeds are usually flat and winged. Aril is absent. Endosperm usually absent, and sometimes sparse.