This small ornamental tree grows 5 to 8 m tall. Its leaves are alternate, acuminate and entire. They are 8 to 12 cm long and 8 cm wide. The pinkish-white flowers are grouped in terminal clusters. They have 5 petals. The fruit is an ovoid brown capsule, 3 to 5 cm long, covered in soft, innocuous spines. Each fruit contains about 50 red seeds.
This species flowers at the end of the rainy season. A single tree can produce over 270 kg of seeds.
It is commonly found along roadsides near people’s homes. It is native to the Amazon basin, where its likely ancestor, Bixa excelsa, still grows. It is found from Mexico to Brazil.
Annatto tree flowers open before dawn, when they are visited by large bees. Smaller bees also visit them in the morning. These insects harvest the abundant pollen from the flowers, which do not produce any nectar. The flowers fade around noon and the corolla drops off in late afternoon.
This tree has nectar-bearing glands on the branches, knots and flower and fruit stems. These glands are active on the branches when the leaves are very young. On the stems, they are active from the time flowering starts until the tree has finished producing fruit. The ants attracted by these sweet secretions protect the tree from herbivorous insects. Birds eat the seeds. Neither vines nor epiphytes grow on this tree.
Uses and effects
Amerindians use this tree and another related species (Bixa urucunara) to prepare body paint. This paint is used for ritual purposes as well as protecting their skin from the sun’s ultraviolet rays and from mosquito bites. The term ‘redskin’ comes from this practice. The orangish red colouring constituent is called bixin.
Annatto tree leaves are refreshing and are used to treat various inflammations, including bronchitis, as well as dysentery and diarrhea. An infusion of the seeds reduces fever. This plant is thought to have a number of other medicinal properties. The fruit is also used as a food colouring and in making cosmetics, including lipstick. The bark is made into rope.