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Herbs, shrubs, rarely erect or lianas. Leaves simple, opposite, ovate to lanceolate, cordate or hastate, usually lobed or toothed, rarely subentire. Cystolith absent. Flowers in terminal, pendulous, racemes or solitary or pairs in the axils of ordinary leaves, blue, yellow, orange-yellow, red or white. Bracts 2, foliaceous, bracteoles spathaceous, enclosing flower buds, mostly persistent. Calyx very short, cup-like, with 10-16 subulate teeth or reduced to a rim. Corolla funnel-form, 5-lobed. Stamens 4, all fertile. Pollen spiraperturate. Ovary seated on disc, 2-locular, 2 ovules in each. Capsules depressed-globose below, abruptly beaked in upper part, 4-seeded, retinacula absent.

Key to the species

Serial Key Reference
1a. Petiole winged; flowers orange-yellow T. alata
1b. Petiole not winged; flowers white, light or dark blue or scarlet-red 2
2a. Erect undershrubs T. erecta
2b. Climbing herbs, scandent shrubs or lianas 3
3a. Flowers scarlet; lianas with glabrous twigs T. coccinea
3b. Flowers white, light to dark blue; twigs not glabrous 4
4a. Flowers white in axillary, solitary or in pairs T. fragrans
4b. Flowers light or dark blue in terminal or axillary racemes T. grandiflora