Macadamia is a genus of four species of trees in the flowering plant family Proteaceae.[1][2] They are indigenous to Australia, native to northeastern New South Wales and central and southeastern Queensland specifically. Two species of the genus are commercially important for their fruit, the macadamia nut /ˌmækəˈdeɪmiə/ (or simply macadamia). Global production in 2015 was 160,000 tonnes (180,000 short tons).[3] Other names include Queensland nut, bush nut, maroochi nut, bauple nut and Hawaii nut.[4] In Australian Aboriginal languages, the fruit is known by names such as bauple, gyndl or jindilli[4] (north of Great Dividing Range) and boombera (south of the Great Range).[citation needed] It was an important source of bushfood for the Aboriginal peoples who are the original inhabitants of the area.
The nut was first commercially produced on a wide scale in Hawaii, where Australian seeds were introduced in the 1880s, and for some time they were the world's largest producer.[5][6] South Africa has been the world's largest producer of the macadamia since the 2010s.
The German-Australian botanist Ferdinand von Mueller gave the genus the name Macadamia in 1857 in honour of the Scottish-Australian chemist, medical teacher and politician John Macadam, who was the honorary Secretary of the Philosophical Institute of Victoria beginning in 1857.[7]
The leaves are arranged in whorls of three to six, lanceolate to obovate or elliptic in shape, 60–300 mm (2+1⁄2–12 in) long and 30–130 mm (1+1⁄8–5+1⁄8 in) broad, with an entire or spiny-serrated margin. The flowers are produced in a long, slender, simple raceme 50–300 mm (2–12 in) long, the individual flowers 10–15 mm (3⁄8–9⁄16 in) long, white to pink or purple, with four tepals. The fruit is a hard, woody, globose follicle with a pointed apex, containing one or two seeds. The nutshell ("coat") is particularly tough and requires around 2000 N to crack. The shell material is five times harder than hazelnut shells and has mechanical properties similar to aluminum. It has a Vickers hardness of 35.[8][9]
Nuts from M. jansenii and M. ternifolia contain cyanogenic glycosides.[29][30] The other two species are cultivated for the commercial production of macadamia nuts for human consumption.
Previously, more species with disjunct distributions were named as members of this genus Macadamia.[2] Genetics and morphological studies published in 2008 show they have separated from the genus Macadamia, correlating less closely than thought from earlier morphological studies.[2] The species previously named in the genus Macadamia may still be referred to overall by the descriptive, non-scientific name of macadamia.
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