They are small to large evergreen trees growing to 2–12 m tall. The leaves are arranged in whorls of three to six, lanceolate to obovate or elliptical in shape, 6–30 cm long and 2–13 cm broad, with an entire or spiny-serrated margin. The flowers are produced in a long slender simple raceme 5–30 cm long, the individual flowers 10–15 mm long, white to pink or purple, with four tepals. The fruit is a very hard woody globose follicle with a pointed apex, containing one or two seeds.
The genus is named after John Macadam, a colleague of botanist Ferdinand von Mueller, who first described the genus. Common names include Macadamia, Macadamia nut,Queensland nut, Bush nut, Maroochi nut, Queen of Nuts and bauple nut; Indigenous Australian names include gyndl, jindilli, and boombera.
The nuts are a valuable food crop. Only two of the species, Macadamia integrifolia andMacadamia tetraphylla, are of commercial importance. The remainder of the genus possess poisonous and/or inedible nuts, such as M. whelanii and M. ternifolia; the toxicity is due to the presence of cyanogenic glycosides. These glycosides can be removed by prolongedleaching, a practice carried out by some Indigenous Australian people in order to use these species as well.
The two species of edible macadamia readily hybridize, and M. tetraphylla is threatened in the wild due to this. The nut was first discovered by Europeans south of Brisbane in 1828 by the explorer and botanist Alan Cunningham. One of the locations where wild nut trees were originally found was at Mount Bauplenear Maryborough in southeast Queensland, Australia. Locals in this area still refer to them as "Bauple nuts". The macadamia nut is the only plant food native to Australia that is produced and exported in any significant quantity.
The first commercial orchard of macadamia trees was planted in the early 1880s by Charles Staff at Rous Mill, 12 km southeast ofLismore, New South Wales, consisting of M. tetraphylla. Besides the development of a small boutique industry in Australia during the late 19th and early 20th century, macadamia was extensively planted as a commercial crop in Hawaii from the 1920s. Macadamia seeds were first imported into Hawaii in 1882 by William H. Purvis. The young manager of the Pacific Sugar Mill atKukuihaele on the Big Island, planted seed nuts that year at Kapulena.
The Hawaiian-produced macadamia established the nut internationally. However, in 2006, macadamia production began to fall in Hawaii, due to lower prices from an over-supply.
Outside of Hawaii and Australia, macadamia is also commercially produced in South Africa, Brazil, California, Costa Rica, Israel,Kenya, Bolivia, New Zealand, Colombia and Malawi. Australia is now the world's largest commercial producer - at approximately 40,000 tonnes of nut in shell per year, with a total global production of 100,000 tonnes.
Macadamia stakeholders try to establish international council or organization to group together members in the macadamia agriculture and businesses. There are several international meeting on the matter. The latest is being arranged in Thailand at the Chaiyaphum Province's Sai Thong National Park of Nong Bua Rawe District called "International Macadamia Symposium" during 25-27 June 2010 featuring academic presentation, new research and studies of macadamia use in nutritional and medical benefits. The organizer group together macadamia stakeholders from various macadamia related background and demonstrate international initiation on macadamia for the use in health, poverty reduction, reforestation, etc as the plant has highly lucrative potential for farmers and agriculturalists in many developing countries. (www.rawedistrict.com for related and additional symposium for macadamia stakeholders and businesses)
Macadamias are highly nutritious nuts. They have the highest amount of beneficial monounsaturated fats of any known nut. They also contain 9% protein, 9% carbohydrate, 2% dietary fiber, as well as calcium, phosphorus, potassium, sodium, selenium, iron,thiamine, riboflavin and niacin.
Macadamia oil is prized for containing approximately 22% of the omega-7 palmitoleic acid, which makes it a botanical alternative to mink oil, which contains approximately 17%. This relatively high content of "cushiony" palmitoleic acid plus macadamia's high oxidative stability make it a desirable ingredient in cosmetics, especially skincare.
The macadamia tree is usually propagated bygrafting, and does not begin to produce commercial quantities of nuts until it is 7–10 years old, but once established, may continue bearing for over 100 years. Macadamias prefer fertile, well-drained soils, a rainfall of 1,000–2,000 mm, and temperatures not falling below 10 °C (although once established they can withstand light frosts), with an optimum temperature of 25 °C. The roots are shallow and trees can be blown down in storms; they are also susceptible to Phytophthora root disease.
The macadamia nut has an extremely hard shell, but can be cracked using a blunt instrument, such as a hammer or rock applied with some force to the nut sitting in a concave surface, or a custom made macadamia nutcracker can be used. Nuts of the "Arkin Papershell" variety crack open more readily.