Bignoniaceae

Growth Form and Habit

Predominantly woody plants, including trees, shrubs, and very commonly lianas (woody vines). A few members are herbaceous vines. Lianas frequently climb using specialized structures such as tendrils (often modified terminal leaflets), grappling hooks, or adventitious roots.

Leaves

Leaves are usually arranged oppositely on the stem, less commonly whorled or rarely alternate. They are typically compound, either pinnately or palmately, although some genera like Catalpa have simple leaves (considered derived from compound ancestors). In many climbing species, the terminal leaflet is modified into a simple or branched tendril. Leaflet margins are usually entire. Stipules are generally absent, though sometimes modified bud scales (pseudo-stipules) are present at the nodes.

Flowers

Flowers are generally large, showy, bisexual, and strongly zygomorphic (bilaterally symmetrical), although some approach radial symmetry. They are typically borne in terminal or axillary racemes, panicles, or cymes.

• Calyx: The sepals are fused (synsepalous) into a tube or bell shape, usually with 5 lobes or teeth, sometimes appearing truncate or splitting irregularly.
• Corolla: The petals are fused (sympetalous) into a tubular, funnel-shaped, or bell-shaped structure, typically ending in 5 lobes that are often arranged into two lips (bilabiate: 2 upper, 3 lower). Corolla color is diverse and often vibrant (yellow, orange, red, pink, purple, white).
• Stamens: Typically 4 fertile stamens, usually in two pairs of different lengths (didynamous), attached to the corolla tube (epipetalous). A fifth stamen is commonly present as a sterile rudiment (staminode), or occasionally absent. Anthers often positioned closely in pairs.
• Ovary: Superior, usually consisting of 2 fused carpels forming 2 locules (chambers). Placentation is typically axile, with numerous ovules per locule. A nectar disk is usually present at the ovary base. The style is single and typically ends in a 2-lobed stigma, the lobes of which are often sensitive and close upon being touched by a pollinator.

Fruits and Seeds

The most characteristic fruit is a dry, dehiscent capsule, which is often elongated and pod-like (linear) or flattened and oblong/oval. The capsule typically splits into two valves (loculicidal or septicidal dehiscence). Less common fruit types include fleshy, indehiscent berries or hard-shelled calabash-like fruits (Crescentia, Kigelia).

Seeds inside the capsules are typically numerous, flattened, and possess distinctive membranous wings that aid wind dispersal. Seeds in fleshy fruits are usually unwinged. Endosperm is absent.

Chemical Characteristics

Members often produce iridoid glycosides, a common feature in the Lamiales order. Quinones, such as lapachol found in Tabebuia (potentially toxic but also with medicinal interest), flavonoids, and tannins are also characteristic of the family. Some species yield dyes or have traditional medicinal applications.