Macadamia
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Macadamia claudiensis
Macadamia grandis
Macadamia hildebrandii
Macadamia integrifolia
Macadamia jansenii
Macadamia ternifolia
Macadamia tetraphylla
Macadamia whelanii
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).
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.
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.” [1] The first commercial orchard of macadamia trees was 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.[2] 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 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.