Macadamia is a nut-bearing tree originating in eastern Australia where it occurs in subtropical rainforests, its natural range extending from coastal northern New South Wales to southeast Queensland.
Through cultivation, its range has widened to other parts of the subtropics, within Australia to just south of the town of Mackay, and outside of Australia to countries such as Hawaii, where it is now a commercially important nut crop.
In natural forests, it may be a tree up to 15 m (50 ft) tall with a straight trunk up to 30 cm (1 ft) in diameter. On open sites and in cultivation it is more typically 5 to 10 m (15 to 30 ft) tall with a short, low-branching trunk and a densely leafy rounded crown. The bark is brown, smooth on young trees, becoming slightly rough on older trees.
The leaves are club-shaped, leathery, 10 to 30 cm ( 4 to 12 in) long, bronze-red when they emerge, age to glossy green and have wavy margins that are sometimes toothed or prickly. They are arranged spirally, in groups of three, towards the ends of the branches and remain on the tree throughout the year.
The flowers are small, creamy-white, petalless tubes, borne in numbers of one to three hundred or more on long, 10 to 30 cm (4 to 12 in) flower spikes, resembling bottle-brushes. They come into bloom from the dry winter to early spring season in its native range, with the spikes hanging, possibly in their thousands, from the ends of the branches and almost hiding the green foliage from view.
Although the flowers are perfect, having both female and male parts, only a few flowers on each spike develop to become fruit. The fruit, when mature, are roundish, up to 2.5 cm (1 in) in diameter, with a prominent nipple and have a smooth green leathery peel, resembling a young lime.
The peel surrounds a round nut with a smooth, glossy brown shell that is very hard and difficult to crack open. It protects an edible, round kernel with creamy, nutty, oily white flesh. As the fruit ripens the peel splits, releasing the nut which falls to the ground.
The fallen nuts are collected from the ground, stored and left to dry for a week before they are eaten or processed. Macadamias are a popular nut that are cultivated commercially and sold for eating as they are or in various snack foods and confectionery, either raw, roasted, salted, unsalted, coated in chocolate, baked in cookies or added to ice-cream. They also yield an edible oil marketed as a high-end salad oil and, more recently, are being used to make a milk substitute sold under the 'Milkadamia' brand.
The flowers produce enough nectar for honey production to be economical, with yields of 25 to 50 kgs (55 to 110 lbs) per colony per season reported for Australia. The pure honey is light to medium amber, of medium density, slow to granulate and with a rich, moderately sweet flavour reminding of butterscotch or malt and caramel.
Macadamia grows naturally and is productive in humid subtropical and tropical mid-elevation climates, generally frost-free areas with annual lows of 11 to 19 °C, annual highs of 21 to 32 °C, annual rainfall of 800 to 3700 mm and a dry season of 4 months or less, extending to 8 months with irrigation or groundwater.
A more cold-hardy species of Macadamia known as the Rough-Shelled Macadamia (Macadamia tetraphylla) has been cultivated successfully in cooler climates, such as the San Francisco Bay area in California. Most Macadamia cultivated in California is a hybrid cross (Macadamia integrifolia x Macadamia tetraphylla)
Macadamia trees may fail to flower and fruit, or do so poorly, in areas where the average low of the coldest month is above 16 °C (61 °F).
New plants are usually produced vegetatively, using cuttings and air-layering (circumposing) techniques. Although new plants can also be started from seed, there is great variation in yield and nut characteristics in seedling trees. Vegetatively produced trees also come into bearing sooner, around two years earlier than seedling trees, when around three to four year old.
Performs best on deep, rich, free-draining clay and loam soils of a moderately acid to neutral nature, generally with a pH of 5.0 to 7.0, and on sites with full to partial sun exposure. It has poor tolerance to slow-draining or waterlogged soils and strong winds.
Yields reported for Australia range from 12 to 15 kgs (26 to 33 lbs) of in-the-shell nuts per tree, per year. However, yields in Hawaii are significantly higher.
It is listed as a weed in at least one reference publication, but there does not appear to be any record of it anywhere as a serious weed, despite it being widely introduced and cultivated in the tropics. It is assessed as a low weed risk species for Hawaii, by the Hawaii Pacific Weed Risk Assessment (HPWRA) project.
The milky sap exuded by part of the plant is high in Hydrogen cyanide (HCN), also known as prussic acid, a poisonous compound that should be treated with caution.
Axtell, B. L & Fairman, R. M 1992, Minor oil crops, Food and Agriculture Organization of the United Nations (FAO), Rome
Barwick, M., et al. 2004, Tropical & subtropical trees : a worldwide encyclopaedic guide, Thames and Hudson, London
Doran, J. C & Turnbull, J. W. 1997, Australian trees and shrubs : species for land rehabilitation and farm planting in the tropics, 2nd ed, Australian Centre for International Agricultural Research (ACIAR), Canberra, Australian Capital Territory
Editors of Sunset Magazine 2012, The New Western Garden Book: The Ultimate Gardening Guide, 9th edition, Sunset Publishing Corporation, California
Elevitch, C. R. & Thaman, R. R. 2011, Specialty crops for Pacific islands, 1st ed, Permanent Agriculture Resources, Hawaii
Elevitch, C. R. 2006, Traditional trees of Pacific Islands: their culture, environment and use, 1st edition, Permanent Agriculture Resources, Hōlualoa, Hawaii
Fellows, P. 1997, Traditional foods : processing for profit, Intermediate Technology, Technical Centre for Agricultural and Rural Co-operation, London
Gunstone, F. D. 2011, Vegetable oils in food technology : composition, properties and uses, 2nd ed, Wiley-Blackwell, Hoboken, New Jersey
Holliday, I. 2002, A field guide to Australian trees, 3rd revised editon, New Holland Publishers, Frenchs Forest, New South Wales
Jensen, M. 1999, Trees commonly cultivated in Southeast Asia : an illustrated field guide, 2nd ed., Food and Agricultural Organisation of the United Nations (FAO) Regional Office for Asia and the Pacific (RAP), Bangkok
Jex-Blake, A. J. 1957, Gardening in East Africa : a practical handbook, 4th ed., Royal Kenya Horticultural Society, Longmans, Green and Company, London
Kennard, W. C. & Winters, H. F. 1960, Some fruits and nuts for the tropics, Miscellaneous Publication No. 801, U.S. Department of Agriculture, Federal Experimental Station, Mayaguez, Puerto Rico
Leech, M. 2013, Bee Friendly: A planting guide for European honeybees and Australian native pollinators, Rural Industries Research and Development Corporation (RIRDC), Canberra, Australian Capital Territory
Macmillan, H. F. 1943, Tropical planting and gardening : with special reference to Ceylon, 5th ed, Macmillan Publishing, London
Page, P. E. 1984, Tropical tree fruits for Australia, Queensland Department of Primary Industries (QLD DPI), Brisbane
Perkins, K. D. & Payne, W. 1981, Guide to the poisonous and irritant plants of Florida, Florida Cooperative Extension Service, Gainesville, Florida
Perry, B. 2010, Landscape plants for California gardens: an illustrated reference of plants for California landscapes, Land Design Publishing, Claremont, California
Randall, R. P. 2002, A global compendium of weeds, R.G. and F.J. Richardson Press, Melbourne
Rosengarten, F. 1984, The book of edible nuts, Walker and Company Publishing, New York
Tindall, H. D. & Rice, L. W. 1990, Fruit and vegetable production in warm climates, International ed., Macmillan, London
Morton, J.F. 1964, Honeybee Plants of South Florida, Proceedings of the Florida State Horticultural Society, Vol 77:415-436.
Watson, B.J., & Moncur, M. 1985, Guideline criteria for determining survival, commercial and best mean minimum July temperatures for various tropical fruit in Australia (Southern Hemisphere), Department of Primary Industries Queensland (DPI QLD), Wet Tropics Regional Publication, Queensland
Wenkam N.S. & Miller C.D. 1965, Composition of Hawaii fruits (Bulletin 135), University of Hawaii, Honolulu
This website is provided for general information only. Iplantz makes no statements, representations or warranties as to the accuracy or completeness of the content of this website and does not accept any liability to you or any other person for the information which is provided or referred to on this website.
In particular, Iplantz does not represent or warrant that any dataset or the data it contains is accurate, authentic or complete, or suitable for your needs. Changes in circumstances after the time of publication may impact the accuracy of datasets and their contents.
To the maximum extent permitted by law, Iplantz accepts no liability whatsoever to any person arising from or connected with the use of or reliance on any information or advice provided on this website or incorporated into it by reference, including any dataset or data it contains. No responsibility is taken for any information or services that may appear on any linked websites.