Bailey, L.H. & Bailey, E.Z. (1976) Hortus Third. A concise Dictionary of Plants Cultivated in the United States and Canada Macmillan Publishing Co, Inc., New York
Description of the genus
Shrubs. Leaves opposite, ovate, entire. Inflorescence a terminal raceme. Flowers red or white. Calyx with 5 coloured petaloid segments. Corolla 5-lobed, two-lipped. Stamens 4, didynamous. Fruit a hairless capsule. Seeds 2-4, spherical, hairless.
Derivation of name: after Mr Thomas Whitfield, collector of plants in West Africa