Macadamia is a genus of four species of trees indigenous to Australia, and constituting part of the plant family Proteaceae. They are native to north eastern New South Wales and central and south eastern Queensland. Three species of the genus are commercially important for their fruit, the macadamia nut // (or simply macadamia), with a total global production of 160,000 tonnes (180,000 short tons) in 2015. Other names include Queensland nut, bush nut, maroochi nut, bauple nut, and Hawaii nut. In Australian Aboriginal languages, the fruit is known by names such as bauple, gyndl, jindilli, and boombera. It was an important source of bushfood for the Aboriginal peoples who were the original inhabitants of the area.
The nut was first commercially produced on a wide scale in Hawaii, where it was introduced in the 1880s, and for some time they were the world's largest producer. South Africa has been the world's largest producer of the macadamia in the 2010s.
The leaves are arranged in whorls of three to six, lanceolate to obovate or elliptic in shape, 60–300 mm (2–10 in) long and 30–130 mm (1–5 in) broad, with an entire or spiny-serrated margin. The flowers are produced in a long, slender, simple raceme 50–300 mm (2–10 in) long, the individual flowers 10–15 mm (0.4–0.6 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 nut shell ("coat") is particularly tough, and requires around 2000 N to crack. The shell material is 5 times harder than hazelnut shells, and has mechanical properties similar to aluminium. It has a Vickers hardness of 35.
- Allan Cunningham was the first European to encounter the macadamia plant.
- German-Australian botanist Ferdinand von Mueller gave the genus the scientific name Macadamia – named after von Mueller’s friend Dr. John Macadam, a noted scientist and secretary of the Philosophical Institute of Australia.
- Walter Hill, superintendent of the Brisbane Botanic Gardens (Australia), observed a boy eating the kernel without ill effect, becoming the first nonindigenous person recorded to eat macadamia nuts.
- King Jacky, aboriginal elder of the Logan River clan, south of Brisbane, Queensland, was the first known macadamia entrepreneur, as his tribe and he regularly collected and traded the macadamias with settlers.
- Tom Petrie planted macadamias at Yebri Creek (near Petrie) from nuts obtained from Aboriginals at Buderim;
- William H. Purvis introduced macadamia nuts to Hawaii as a windbreak for sugar cane.
- The first commercial orchard of macadamias was planted at Rous Mill, 12 km from Lismore, New South Wales, by Charles Staff.
- Joseph Maiden, Australian botanist, wrote, "It is well worth extensive cultivation, for the nuts are always eagerly bought."
- The Hawaiian Agricultural Experiment Station encouraged planting of macadamias on Hawaii's Kona District, as a crop to supplement coffee production in the region.
- Tom Petrie begins trial macadamia plantations in Maryborough, Queensland, combining macadamias with pecans to shelter the trees.
- Ernest Van Tassel formed the Hawaiian Macadamia Nut Co in Hawaii.
- Tassel leased 75 acres (30 ha) on Round Top in Honolulu and began Nutridge, Hawaii's first macadamia seed farm.
- Tassel established a macadamia-processing factory on Puhukaina Street in Kakaako, Hawaii, selling the nuts as Van's Macadamia Nuts.
- Winston Jones and J. H. Beaumont of the University of Hawaii's Agricultural Experiment Station reported the first successful grafting of macadamias, paving the way for mass production.
- Steve Angus, Murwillumbah, Australia, formed Macadamia Nuts Pty Ltd, doing small-scale nut processing.
- A large plantation was established in Hawaii.
- Castle & Cooke added a new brand of macadamia nuts called "Royal Hawaiian", which was credited with popularizing the nuts in the U.S.
- Australia surpassed the United States as the major producer of macadamias.
- South Africa surpassed Australia as the largest producer of macadamias.
- The way that macadamia nuts were served one day on Korean Air Flight 86 at John F. Kennedy International Airport in New York City led to an infamous "nut rage incident", which gave the nuts high visibility in the South Korean economy and marked a sharp increase in consumption there.
- Macadamia integrifolia Maiden & Betche
- Macadamia jansenii C.L.Gross & P.H.Weston
- Macadamia ternifolia F.Muell.
- Macadamia tetraphylla L.A.S.Johnson
Previously, more species with disjunct distributions were named as members of this genus Macadamia. Genetics and morphological studies published in 2008 show they have separated from the genus Macadamia, correlating less closely than thought from earlier morphological studies. The species previously named in the genus Macadamia may still be referred to overall by the descriptive, non-scientific name of macadamia.
- (C.L.Gross & B.Hyland) & A.R.Mast; synonym, base name: Macadamia claudiensis C.L.Gross & B.Hyland
- (J.A.McDonald & R.Ismail) P.H.Weston & A.R.Mast; synonym, base name: Macadamia erecta J.A.McDonald & R.Ismail
- (C.L.Gross & B.Hyland) P.H.Weston & A.R.Mast; synonym, base name: Macadamia grandis C.L.Gross & B.Hyland
- (Steenis) P.H.Weston & A.R.Mast; synonym, base name: Macadamia hildebrandii Steenis
- (F.M.Bailey) P.H.Weston & A.R.Mast; synonyms: base name: Helicia whelanii F.M.Bailey, Macadamia whelanii (F.M.Bailey) F.M.Bailey
- Catalepidia P.H.Weston, formerly Macadamia until 1995
- Catalepidia heyana (F.M.Bailey) P.H.Weston; synonyms: base name: Helicia heyana F.M.Bailey , Macadamia heyana (F.M.Bailey) Sleumer
- Virotia L.A.S.Johnson & B.G.Briggs, formerly Macadamia until the first species renaming began in 1975 and comprehensive in 2008
- (Virot) P.H.Weston & A.R.Mast; synonym, base name: Macadamia angustifolia Virot
- (Guillaumin) P.H.Weston & A.R.Mast; synonym, base name: Roupala francii Guillaumin
- (Guillaumin) L.A.S.Johnson & B.G.Briggs (1975 type species); synonym, base name: Kermadecia leptophylla Guillaumin
- Virotia neurophylla (Guillaumin) P.H.Weston & A.R.Mast; synonyms: base name: Kermadecia neurophylla Guillaumin, Macadamia neurophylla (Guillaumin) Virot
- (Vieill.) P.H.Weston & A.R.Mast; synonym, base name: Roupala rousselii Vieill
- (Brongn. & Gris) P.H.Weston & A.R.Mast; synonym, base name: Roupala vieillardii Brongn. & Gris
Three of the four species—Macadamia integrifolia, Macadamia ternifolia, and Macadamia tetraphylla—are of commercial importance. The other species, M. jansenii, produces poisonous nuts resulting from toxic amounts of cyanogenic glycosides.
The macadamia tree is usually propagated by grafting, and does not begin to produce commercial quantities of seeds 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 (40–80 in), and temperatures not falling below 10 °C (50 °F) (although once established, they can withstand light frosts), with an optimum temperature of 25 °C (80 °F). The roots are shallow and trees can be blown down in storms; like most Proteaceae, they are also susceptible to Phytophthora root disease. As of 2019, the macadamia nut is the most expensive nut in the world, which is attributed to the slow harvesting process.
A Macadamia integrifolia / M. tetraphylla hybrid commercial variety is widely planted in Australia and New Zealand; it was discovered by Dr. J. H. Beaumont. It is high in oil, but is not sweet. New leaves are reddish, and flowers are bright pink, borne on long racemes. It is one of the quickest varieties to come into bearing once planted in the garden, usually carrying a useful crop by the fourth year, and improving from then on. It crops prodigiously when well pollinated. The impressive, grape-like clusters are sometimes so heavy, they break the branchlets to which they are attached. In commercial orchards, it has reached 18 kg (40 lb) per tree by eight years old. On the downside, the macadamias do not drop from the tree when ripe, and the leaves are a bit prickly when one reaches into the interior of the tree during harvest. Its shell is easier to open than that of most commercial varieties.
A pure M. tetraphylla variety from Australia, this strain is cultivated for its productive crop yield, flavor, and suitability for pollinating 'Beaumont'.
A South African M. integrifolia / M. tetraphylla hybrid cultivar, it has a sweet seed, which means it has to be cooked carefully so that the sugars do not caramelise. The sweet seed is usually not fully processed, as it generally does not taste as good, but many people enjoy eating it uncooked. It has an open micropyle (hole in the shell) which may let in mould. The crack-out percentage (ratio of nut meat to whole nut, by weight) is high. Ten-year-old trees average 22 kg (50 lb) per tree. It is a popular variety because of its pollination of 'Beaumont', and the yields are almost comparable.
A M. integrifolia / M. tetraphylla hybrid, this is a rather spreading tree. On the plus side, it is high yielding commercially, 17 kg (37 lb) from a 9-year-old tree has been recorded, and the nuts drop to the ground. However, they are thick-shelled, with not much flavor.
In 2018, South Africa was estimated to remain the world's leading producer of macadamia nuts with 54,000 tonnes out of global production of 211,000 tonnes. In 2015, South Africa produced 48,000 tonnes (53,000 short tons) compared to Australia's 40,000 tonnes and the total global production of 160,000 tonnes (180,000 short tons). Macadamia is also commercially produced in Brazil, United States (California and Hawaii states), Costa Rica, Israel, Kenya, China, Bolivia, New Zealand, Colombia, Guatemala and Malawi.
The first commercial orchard of macadamia trees was planted in the early 1880s by Rous Mill, 12 km (7.5 mi) 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, who planted seeds that year at Kapulena. The Hawaiian-produced macadamia established the well-known seed internationally, and in 2017 Hawaii produced over 22,000 tonnes.
In 2019, researchers collected samples from hundreds of trees in Queensland, and compared the genetic profiles to samples from Hawaiian orchards. They determined that essentially all the Hawaiian trees must have descended from a small population of Australian trees from Gympie, possibly just a single tree. This lack of genetic diversity in the commercial crop puts it at risk of succumbing to pathogens (as has happened in the past to banana cultivars). Growers may seek to diversify the cultivated population, by hybridizing with wild specimens.
Nuts food and nutrition
The seeds (nuts) are a valuable food crop.
In a 100-gram amount, macadamia nuts provide 740 Calories and are a rich source (20% or more of the Daily Value, DV) of numerous essential nutrients, including thiamine (104% DV), vitamin B6 (21% DV), manganese (195% DV), iron (28% DV), magnesium (37% DV), and phosphorus (27% DV) (table). Macadamia nuts are 76% fat, 14% carbohydrates, including 9% dietary fiber, and 8% protein (table).
Compared with other common edible nuts, such as almonds and cashews, macadamias are high in total fat and relatively low in protein (table). They have a high amount of monounsaturated fats (59% of total content, table) and contain, as 17% of total fat, the monounsaturated fat, omega-7 palmitoleic acid.
Toxicity in dogs
Macadamias are toxic to dogs. Ingestion may result in macadamia toxicity 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, with full recovery usually within 24 to 48 hours.
The trees are also grown as ornamental plants in subtropical regions for their glossy foliage and attractive flowers. The flowers produce a well regarded honey. The wood is used decoratively for small items. Macadamia species are used as food plants by the larvae of some Lepidoptera species, including Batrachedra arenosella.
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