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| Macadamia nut in its shell and a roasted nut |
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 and Macadamia 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 prolonged leaching, a practice used by some Indigenous Australian people for 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 described 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 Bauple near 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 of Lismore, New South Wales, consisting of M. tetraphylla. Besides the development of a small boutique industry in Australia during the late 19th and early 20th centuries, 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 at Kukuihaele 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 – accounting for roughly 40% of the approximately 100,000 tonnes of nut in shell per year produced globally.
Compared to other common edible nuts such as almonds and cashews, macadamias are high in fat and low in protein.[9] They have the highest amount of beneficial monounsaturated fats of any known nut, but also contains approximately 22% of omega-7 palmitoleic acid, which has biological effects similar to saturated fat. They also contain 9% protein, 9% carbohydrate, and 2% dietary fiber, as well as calcium, phosphorus, potassium, sodium, selenium, iron, thiamine, riboflavin and niacin.
Macadamias are toxic to dogs. Ingestion may result in macadamia nut toxicosis, which is marked by weakness and hind limb paralysis with the inability to stand, occurring within 12 hours of ingestion. Depending on the quantity ingested and size of the dog, symptoms may also include muscle tremors, joint pain and severe abdominal pain. In high doses of toxin, opiate medication may be required for symptom relief until the toxic effects diminish. Full recovery is usually within 24 to 48 hours.
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 for skincare.
The trees are also grown as ornamental plants in subtropical regions for their glossy foliage and attractive flowers. Macadamia species are used as food plants by the larvae of some Lepidoptera species, including Batrachedra arenosella.
Macadamia nuts are often used by law enforcement to simulate crack cocaine in drug stings. When chopped, the nuts resemble crack cocaine in color.
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