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Macadamia integrifolia foliage and nuts
Plant Info
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Scientific classification
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Type Species
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Species
Macadamia claudiensis Macadamia grandis Macadamia hildebrandii Macadamia integrifolia Macadamia jansenii Macadamia ternifolia Macadamia tetraphylla Macadamia whelanii
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Synonyms
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Macadamia is a genus of eight species of flowering plants in the family Proteaceae, with a disjunct distribution native to eastern Australia (seven species) and Indonesia Sulawesi (one species, M. hildebrandii).

Macadamia integrifolia flowers

They are small to large evergreen trees growing to 6–40 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, who was a colleague of the botanist Ferdinand von Mueller who first described the genus. Common names include Macadamia, Macadamia nut, Queensland nut, Bush nut, Maroochi nut and Bauple nut; Indigenous Australian names include Kindal Kindal and Jindilli.

Cultivation and uses

Macadamia nut in its shell and a roasted nut

The nuts are a valuable food crop. Only two of the species, M. integrifolia and M. 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 carried out by some Indigenous Australian people in order to use these species as well.

The two species of edible Macadamia readily hybridise, and M. tetraphylla is threatened in the wild due to this. Wild nut trees were originally found at Mt. Bauple near Maryborough in SE 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.

Joseph Maiden, Australian botanist, wrote in 1889 "It is well worth extensive cultivation, for the nuts are always eagerly bought." The first commercial orchard of Macadamia trees were planted in the early 1880s by Mr Charles Staff at Rous Mill, 12 km south east 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 Century, macadamia was extensively planted as a commerial crop in Hawaii from the 1900s. The Hawaiian produced macadamia established the nut internationally.

The Macadamia tree is usually propagated by grafting, 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. Outside of Australia, commercial production is also established in Hawaii, Brazil, California, Costa Rica, Israel, Kenya, Bolivia, New Zealand, South Africa and Malawi. Australia is now the world's largest commercial producer - at approximately 40,000 tonnes of nut in shell per year.

The Macadamia nut's kernel is extremely hard to mine out of its shell (it requires about 300 psi or 2000 kPa to crack), but after some time in a warm and dry place the shell may develop big cracks. The nut can be opened then with a screwdriver, though the warm dry conditions also reduce the nutritional value of the nut. The shell is most easily cracked with a metalworking bench vice, but care must be taken not to crush the kernel in the process. The nuts can be opened simply by locating the seam line on the shell (This seam line can be located by looking carefully at the shell) and placing a knife blade on the line and tapping with a hammer. The shell will open and allow the nut to be removed whole. A safer and quicker alternative is to use a Ratchet style PVC pipe cutter. Place the cutter blade on the seam line and ratchet it closed—the shell will split and allow the nut to be removed. When nuts have dried for a period of time the kernel will fall out (with green or fresh nuts the kernel may stick in the shell). The nuts can also be smashed open with a hammer or heavy solid kitchen tool. Boiling the nuts for a few minutes in a pot until the nuts rise to the surface is also a good way as it causes the nuts to crack. Nuts of the "Arkin Papershell" variety, cultivated by retired stockbroker Morris Arkin, each have a blemish or small crack somewhere on the shell, and the shell will crack open readily if left for a few days, or if struck properly with a hammer.

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.

Macadamia nuts form the staple diet of the Hyacinth Macaw in captivity. These large parrots are one of the few animals, aside from humans, capable of cracking and shelling the nut.

Macadamia nuts are toxic to dogs. Ingestion may result in Macadamia nut toxicosis, which is marked by weakness with the inability to stand within 12 hours of ingestion. Recovery is usually within 48 hours .

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.

External links

• Flora of Australia: Macadamia
• Template:APNI
• Australia's most delicious bush nut