There are fifteen species in the genus Allamanda, all originating from South America, although many are now widely cultivated in the tropics and subtropics, and some have even become invasive species in parts of Australia. All species have large, trumpet-shaped flowers, arranged in terminal inflorescences and grow as shrubs or shrubby climbers, using surrounding vegetation for support. Most species have yellow flowers, but the Brazilian Allamanda blanchetii has reddish-purple flowers. All allamandas need plenty of sun and warm conditions, with night-time minimum temperatures of 21 degrees Celsius, although these can be reduced to about 15 degrees Celsius, if kept on the dry side. The propagation of allamandas is easily done using cuttings. Pests, such as mealy bug, red spider mite, thrip and glasshouse leaf hopper, can be serious problems, particularly under glass.
Two other Brazilian species are grown in the glasshouses at Oxford Botanic Garden, Allamanda schottii and Allamanda cathartica. Allamanda schottii grows into a small shrub, reaching about 3.5 metres tall. The flowers are bright yellow and are followed by prickly fruits which are sometimes used in flower arranging. However, all allamanda fruits are poisonous and the plant's milky sap, typical of the family, may cause skin irritation in some people.
Allamanda cathartica, commonly known as the golden trumpet vine, is very vigorous, reaching over six metres tall and, in cultivation, it is best constrained by training the vine on wires or over a pergola. Plants may also be clipped to form shrubs or hedges. There are two cultivars, 'Hendersonii' and 'Williamsii'. The former is more common and differs from the standard in that it has larger flowers, whilst 'Williamsii' is fragrant with semi-double flowers but is rarely seen. Allamanda cathartica is abundant in Guyana, where it grows in mangrove swamps and along lowland streams. If growing in temperate climates, glasshouse conditions are required and although they can be grown in pots, planting out is probably best due to their vigour.
In 2009 Allamanda calcicola was described as a new, endemic species to Brazil. It had been overlooked in the 1970s, when it was mistaken for very similar looking species. The species is found in south-western Bahia and northern Minas Gerais where it grows in seasonally dry, semi-arid habitats on limestone outcrops.
The Swedish naturalist Carolus Linnaeus used the name Allamanda to commemorate Frédéric-Louis Allamand, a Swiss botanist who collected plants in northern South American in the mid-eighteenth century.
De Souza-Silva RF and Rapini A 2009. Allamanda calcicola (Apocynaceae), an overlooked new species from limestone outcrops in the States of Minas Gerais and Bahia, Brazil. Kew Bulletin 64: 171-174.
Llamas KA 2003. Tropical flowering plants. Timber Press.
Phillips R and Rix M 1997. Conservatory and indoor plants. Pan Books.