Macadamia (Part 23)
Smooth macadamias. Medowie, NSW. © JPM, 2022.
You northerners can keep your walnuts, almonds and pecans. Macadamia nuts are better anyway!
Adored by the First Nation tribes of south-east Queensland and northern New South Wales as bauple, bopple, gyndl, jindilli and boombera for millennia prior, these highly sought-after morsels were botanically catalogued by German botanist Ferdinand von Mueller in 1857. He named them Macadamia (M.) after one of his chief financial sponsors, the Scottish-born chemist, teacher, politician and secretary of the failed Bourke & Wills expedition, John Macadam.
There are four native species. Two are poisonous and inedible: the Maroochy nut (M. ternifolia) and the recently (1991) classified Bulberin nut (M. jansenii). These two species will be covered in the caution below. The other two have become the backbone of the billion-dollar world-wide macadamia industry: the smooth macadamia (M. integrifolia) and the rough macadamia (M. tetraphylla). These latter two species have been cross-bred over the last century, particularly by the Americans in Hawaii, resulting in a myriad of interesting commercial cultivars.
Habitat and Range
Macadamias in the wild are a rain forest understorey tree, preferring rich, well-draining soils and annual rainfall of 1000-2000 mm. They struggle in cold climes dropping to less than 10°C, preferring temperatures of 25°C, but established trees can resist the odd light frost. In Australia they are most common in the Gympie-Fraser coast region, extending down the Great Dividing Range into northern and central New South Wales, having patchy distribution between Townsville and Cairns in north Queensland. They were first introduced to Hawaii in the 1880s to function as a wind break for sugar cane, but the Americans loved the nuts so much that breeding for commercialisation was well underway by the 1920s. Australian commercialisation did not commence until the 1960s, mostly utilising Hawaiian cultivars, and South Africa overtook Australia as the largest exporter of the nut in 2010. Macadamias may now be found in backyards across the country and internationally.
Figure 1. Distribution of Macadamia (all species) across the continent. Atlas of Living Australia.
Key Identifying Features
- Medium to large sized trees, 3-15 metres in height
- Leaves grow in 'whorls' at the branch tips, usually in groups of 3 or 4
- Leaves are 8-25 cm long and can be smooth, wavy edged (M. integrifolia) or serrated (M. tetraphylla), or any combination of the two.
- Flowers emerge any time of year (but mostly in June-August) on a long, slender stalk
- Flowers are four-petaled and yellow-white
- Flowers are highly attractive to bees
- Fruits bud from the stalks in clusters of 1-12
- Unripe fruit is green, often with a protruding 'nose'
- Fruit may have smooth (M. integrifolia) or rough (M. tetraphylla) skin
- Fruits drop from the tree when ripe and split open to reveal the brown, insanely hard inner shell
- Shells must be cracked open with immense force to reveal the creamy, white kernel
Figure 2. Smooth macadamia (M. integrifolia) trees in a commercial orchard. Medowie, NSW. © JPM, 2022.
Figure 3. Smooth macadamia (M. integrifolia) foliage 'whorls' in threes. Medowie, NSW. © JPM, 2022.
Figure 4. Rough macadamia (M. tetraphylla) displaying its whorls of 3-4 leaves. Atlas of Living Australia. © G. Tasney, 2021.
Flowers emerge from the branches on long stalks (racemes), each of which bears several scores of flowers at once. The flowers are sweet scented and highly attractive to bees, also producing an excellent quality, fragrant honey. Once pollinated, the fruits bud from these racemes and become the dangling dozens pictured in the header image at the top of this article. Fruit will begin to split when ripe, either falling from the tree completely, or releasing the hard, inner shell which falls to the ground. These inner shells require ~2,000 Nm of force to break open, one of the hardest plant substances known. Once cracked, however, they reveal their desirable, creamy, oily kernel which ought to be greedily devoured on the spot.
Figure 5. The long flower racemes of a smooth macadamia (M. integrifolia). Atlas of Living Australia. © M. Fagg, 2016.
Figure 6. Flowers wilt and disappear after pollination, leaving behind long, white pistils and budding fruit. Medowie, NSW. © JPM, 2022.
Figure 7. Close-up of the budding, young fruits. I count approximately 13 on this stalk. Medowie, NSW. © JPM, 2022.
Figure 8. Close-up of unripe nuts on a smooth macadamia. Medowie, NSW. © JPM, 2022.
Figure 9. Mature fruit on a rough macadamia (M. tetraphylla). Notice the difference in texture of the fruit husk compared with figure 8 above. Smooth macadamias may split open in this same way when ripe. Atlas of Living Australia. © M. Fagg, n.d.
Figure 10. Closeup of the rock-hard, inner shell. This nut was left on the ground where I found it, since this was a commercial farm and pick-your-own was forbidden. Medowie, NSW. © JPM, 2022.
Figure 11. One the cockatoos prepared earlier. This nut was left on the ground where I found it, since this was a commercial farm and pick-your-own was forbidden. Medowie, NSW. © JPM, 2022.
Macadamias are loved for their oily, creamy nut kernels the world over, even inducing the infamous Korean "nut rage" incident (see here).
Trees take 10-15 years to begin producing nuts, so keep that in mind before deciding to invest in this potentially profitable plant. Ripe macadamias will usually have split husks (outer shells) on the tree, the inner side of which will stain brown; any husk which has a white or sticky inner side is under-ripe (for pictures see Ohiwa Macadamias). Over time, the sugars in the kernel convert to oil, making them float (Ohiwa Macadamias).Thus, extracted kernels may be placed in a glass of water to test for ripeness.
Macadamias should never be stored in their outer husks as these husks are high in plant sugars which attract mould, potentially damaging the inner shell and kernel (Ohiwa Macadamias). Thus, husking should occur within 24 hours of harvest. Home gardeners should check for fallen or split nuts on the tree at least weekly, if not daily, and immediately de-husk any that are collected. Ohiwa Macadamias recommend a two-stage drying process to reduce the water content of the hard shells from 27% (fresh) to 4% to make cracking easier. Inner shells should first be left to dry in a shaded but breezy place (Ohiwa suspends onion bags full of macadamias) for 6-8 weeks. After this, they need to be dried further by exposure to hot (30 degrees C) and dry (less than 30% humidity) air. A home gardener could use a dehumidifier in a closed, warm room for a few days to achieve a similar effect. Rotate drying shells regularly to inhibit humidity buildup and mould growth.
Macadamia nuts may be eaten raw or roasted, salted or unsalted, they are absolutely delicious mixed with vanilla bean. They can be added to salads, cakes, pastries and desserts of all kinds, and blended into macadamia butter as a spread. Nuts can also be pressed for their nutritious oil.
Figure 12. 100% pure macadamia oil. We go to Medowie to stock up on this about twice per year. © JPM, 2022.
According to Wikipedia, "raw macadamia nuts are 1% water, 14% carbohydrates, 76% fat, and 8% protein. 100 grams of raw macadamia nuts provides approximately 740 kilocalories, are a rich source of numerous essential nutrients, including thiamine (104% DI), vitamin B6 (21% DI), other B vitamins, manganese (195% DI), iron (28% DI), magnesium (37% DI) and phosphorus (27% DI). Compared with other common edible nuts, such as almonds and cashews, macadamias are high in total fat and relatively low in protein. They have a high amount of monounsaturated fats (59% of total content) and contain, as 17% of total fat, the monounsaturated fat, omega-7 palmitoleic acid."
They are a phenomenal, energy- and nutrient-dense food. No wonder they were highly esteemed by the First Nation tribes and a prized trade commodity, in those days and still today.
As covered above, two of the true macadamias (the Maroochy nut, M. ternifolia, and the Bulberin nut, M. jansenii) are poisonous, containing bitter cyanogenic glycosides. Since these species are uncommon, it is unlikely they will be encountered in the wild. They tend to have smaller foliage and fruits when compared with the edible cultivars. M. ternifolia also has pink flowers.
Figure 13. The poisonous Maroochy nut (M. ternifolia) foliage and flowers, not to be confused with the "Maroochy" cultivar of the smooth macadamia (M. integrifolia). © I. Mcmaster, 2020.
Figure 14. The poisonous Bulberin nut (M. jansenii), limited to a two endangered stands of less than 100 wild trees, mostly near Miriam Vale near Gladstone. You are unlikely to encounter this species unless you are actively searching for it. Atlas of Living Australia. © M. Fagg, 2008.
Look-alikes - Edible and Inedible
Australia is also home to dozens of similar trees of related genera which resemble macadamia. Hicksbeachia pinnatifolia, otherwise known as the bopple nut, is limited to small areas of SEQ and Cape York has red fruit with edible nuts inferior in flavour to macadamia; the little-studied Lasjia (L.) genus very much resembles macadamia, except for the thinner seed shells, and at least four species were eaten: L. whelanii and L. grandis were eaten by the Bama tribe of the Bellenden Ker rainforest region, L. claudiensis by the Umpila of the Iron Range, and L. hildebrandii by Sulawesi (Indonesian) islanders; Athertonia diversifolia, the Atherton oak, has blue-black fruit with an edible nut kernel, common in the Cairns/Atherton region; Catalepidia heyana, Hey's nut, has a red fruit and a black shell but is inedible; lastly is Floydia praealta, the ball nut, a vulnerable tree of northern NSW, has similar foliage and flowers but brown-husked, inedible nuts rather than the green nuts of true macadamias.
I may cover some of these in detail in later articles of this series, but owing to the fact they are not terribly common plants, their priority is low.