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A genus of about twenty species (perhaps fewer), mostly in the warmer parts of E. Asia and Malaysia, but the almost glabrous T. difforme is N. American. Leaves opposite, entire, they and the stems exuding a milky juice when cut. Flowers in the cultivated species white or yellowish, fragrant, borne in terminal cymes. Calyx small, five-lobed. Corolla with a slender tube and five spreading lobes overlapping each other to the right and convolute in the bud. Stamens inserted on the tube, their anthers united and attached to the stigma, included or slightly exserted. Ovary consisting of two carpels, each developing into a slender follicle.
Both species need the protection of a wall, and a good soil. The addition of peat to the soil when planting is an advantage. Increased by cuttings taken in July or August.