Anacardium occidentale is an evergreen tree endemic to regions of central and north-eastern Brazil with pronounced dry seasons, e.g., the restinga and cerrado. Long before European colonisation, this plant was utilised by indigenous peoples in Brazil for food, medicine and fuel, whilst individual trees with desirable characteristics were selected, protected and moved. By the mid-sixteenth century, the Portuguese had moved the tree to India, from whence it was probably introduced to Africa and southeast Asia. The name cashew is apparently a mishearing of the Portuguese name caju by the English pirate-naturalist William Dampier, as it first appears in Dampier’s A voyage to New Holland, &c. in the year, 1699 (1703). The Portuguese took their name from a Tupi name acaju.
Wild cashew trees are usually stout and twisted, but can reach over 10 metres in height. Trees from which the familiar cashew nuts are harvested are usually dwarfed by grafting. On individual Anacardium occidentale trees, the small, star-like, insect-pollinated flowers are a mixture of many males and few hermaphrodites. Once a hermaphrodite flower is fertilised, a kidney-shaped, single-seeded fruit develops, followed by expansion of the flower stalk to produce a fleshy, brightly coloured, pear-shaped structure, commonly called a ‘cashew apple’. Interpretation of the hard fruit and the soft cashew apple can cause confusion. Whilst in Surinam, the late seventeenth-century artist-naturalist Maria Sibylla Merian portrayed Anacardium occidentale with mature fruit attached directly to the branch, rather than separated by the cashew apple.
The familiar cashew nut is the plant’s seed. They are sold separated from the fruit, as the wall of the latter contains an irritant oil that may be highly allergenic. Cashews nuts are consumed worldwide, having become important parts of cuisines beyond the native range of Anacardium occidentale. In 2018, global production of cashew kernels was approximately 5.9 million tonnes, with 70% produced by three countries – Vietnam, India and Côte d'Ivoire.
Cashew apples are aromatic and slightly astringent, but are consumed fresh, as juice or made into sweets. In contrast to the nut, Brazil accounted for nearly 90% of the 1.7 million tonnes of cashew apples grown in 2018.
An important by-product of cashew processing is the oil-rich fruit wall. When processed, these walls yield industrial quantities of chemicals, such as anacardic acid, cardol and cardanol, which are important for making resins and composite materials. Traditionally, cashew fruit oil has been used as medicine and as a wood preservative.
Freitas, BM and Paxton, RJ 1998. A comparison of two pollinators: the introduced honey bee Apis mellifera and an indigenous bee Centris tarsata on cashew Anacardium occidentale in its native range of NE Brazil. Journal of Applied Ecology 35: 109-121.
Johnson, D 1973. The botany, origin, and spread of the cashew, Anacardium occidentale L. Journal of Plantation Crops 1: 1-7.
Mitchell, JD and Mori, SA 1987.The cashew and its relatives (Anacardium: Anacardiaceae). Memoirs of the New York Botanical Garden 42: 1-76.