MACADAMIA: CHARACTERISTICS, HABITAT, BENEFITS, CULTIVATION, DISEASES - BIOLOGY - 2025

Macadamia is a genus that includes about ten species, of which only two of them are edible (Macadamia integrifolia and Macadamia tetraphylla) since the others are considered toxic. It belongs to the Proteaceae family, and of the nuts, it is the most gourmet and the most used in the kitchen.

The species of this genus are trees that measure a maximum of 20 m in height and 15 m in diameter. They are evergreen, with leathery, shiny leaves that reach up to 30 cm. The flowers also have a leathery texture and are white or pink. The fruits are a nut that only ripens until the moment it falls from the tree, so its harvest cannot be done before.

Macadamia tetraphylla flowers. Source: Krzysztof Ziarnek, Kenraiz

Its flavor is delicate, a little sweet, which makes them ideal to be used in baking. In addition, these nuts have a high content of high quality oil that is highly valued in the cosmetic industry.

It is important to know that the multiple benefits of macadamia should only be directed towards humans, since these nuts are toxic to animals such as dogs, which can suffer from vomiting, weakness, lack of coordination, hyperthermia and tremors.

characteristics

Appearance

These are trees that reach up to 20 m high and 15 m in diameter. They maintain a permanent foliage and, both the color of the flowers, the size of the nut and the thickness of the shell, varies between each species.

It is a slow-growing genus, where cultivable species can last 5 years to produce the first harvest.

Leaves

The leaves of the macadamias are leathery in texture, shiny in appearance, measuring 20 to 30 cm. They are arranged in a spiral, are petiolate, green, purple or reddish in color. The margins may be serrated and may or may not have spines.

Macadamia integrifolia leaves. Source: Forest & Kim Starr

flowers

Most of the flowers of these species are pink or white. They develop in cluster-type inflorescences.

Fruit

The flower clusters can develop up to 20 fruits each. Although it is not a true nut, the fruit contains a round shiny seed of about 25 mm. The peel is leathery, green in color and splits longitudinally during ripening.

Macadamia nuts in different stages. Source: Forest & Kim Starr

Taxonomy

-Kingdom: Plantae

-Subreino: Viridiplantae

-Superfphylum: Embryophyta

-Phylum: Tracheophyta

-Class: Spermatopside

-Superorden: Proteanae

-Order: Proteales

-Family: Proteaceae

-Subfamily: Grevilleoideae

-Tribe: Macadamieae

-Gender: Macadamia F. Von Mueller (1858)

The edible species are:

Macadamia integrifolia

It is the most widely cultivated species because it produces high quality fruits and its nut has a smooth texture. It also has leaves with few thorns. Within this species are some cultivars such as Kakea, Makai, Makua, Pohala, and Keauhou.

Macadamia integrifolia trees. Source: Forest & Kim Starr

Macadamia tetraphylla

It is a lower quality species of walnut due to its rough texture and leaves with many thorns. In this species the Cate and Elimbah varieties are obtained.

Habitat and distribution

It is a genus native to Australia, especially between the subtropical and coastal region. However, today these plants have been widely cultivated in many parts of the world such as South Africa, South America, Israel and the United States.

It lives in places where there are annual temperatures from mild to hot, precipitation is high and frosts do not occur during winter. It is distributed from 400 to 1200 meters above sea level.

Health benefits

Macadamia nuts are a complete food as they contain vitamins, minerals, and antioxidants. So much so that a single serving contains 58% of the RDA for manganese and 23% vitamin B1 (thiamine).

Walnuts contain a good number of nutrients and monounsaturated fats. They are low in carbohydrates and protein, as they only contain 2% in an ounce. On the other hand, they are rich in omega-9 monounsaturated fatty acids (the same one found in olive oil) and oleic acid.

Macadamia nuts are a complete and healthy food. Source: Forest & Kim Starr

Of the total fat content in the walnut, only 14% corresponds to saturated fat. Macadamia nuts have proven beneficial for weight loss and waist size reduction.

In fact, consuming these nuts as part of the diet or as a substitute for another food for five weeks has been shown to promote the loss of approximately 1.4 pounds (650 grams) and the reduction of half an inch (1.25 cm) waist. With these data, it is more favorable to consume a bunch of walnuts than a bran muffin if you are following a plan to lose weight.

Another benefit is that they contain the same amount of oleic acid that is in olive trees, so that they provide a good amount of healthy fat, while the carbohydrate contribution is very low.

In this sense, the consumption of the macadamia nut reduces the risk of suffering cardiovascular diseases, hypertension, metabolic syndrome, abdominal obesity and high fasting glucose.

On the other hand, the consumption of macadamia nuts has been associated with the reduction of diabetes in women, gallstones in women and men, reduction of oxidative stress, inflammation, as well as vascular benefits related to coronary heart disease.

Macadamia bunches can have about 20 fruits. Source: Forest & Kim Starr

Applications

Macadamia shells are mixed in compost bins to serve as mulch as fertilizer. While in Japan, the oil of these plants is used to make soaps, sunscreens, shampoo, and the remainder can be used to make food for some animals.

These nuts are used in the preparation of cookies, breads, pastries in general, in fruit salads or green salads.

Culture

Weather

Taking into account the origin of this genus, it can be said that macadamia supports places where there is high rainfall, high humidity occurs and there are no frosts.

However, macadamia can be adapted to locations far from the tropics or subtropics. In this way, the macadamia has a relative tolerance to the cold and can withstand mild frosts as the specimens become adults.

On the other hand, macadamia tolerates high temperatures (between 18 and 29 ° C), but above 32 ° C there can be undesirable consequences. In these cases, the tree must be protected with shade nets, or cultivated together with other species that provide shade.

Light

Macadamia requires a minimum of three hours of light a day.

Floor

Generally, macadamia is adapted to deep soils with high nutritional content, but they can also grow well in poor or caked soils.

Regarding the pH, the macadamia prefers acid soils between 4.5 and 6.5, so it is better not to plant it in alkaline soils to avoid losses in the future. However, a small correction to soil pH can be applied through agricultural strategies.

Irrigation

It is considered that the irrigation of the macadamia must be abundant since in the places of origin the annual rainfall is between 1500 and 3000 mm. Similarly, macadamia also has a certain tolerance to water stress (up to two months of drought).

Sowing

There are certain very important characteristics to take into account for the planting process. For example, these plants have a very delicate and sensitive root that can be affected during transplantation, so their handling must be done with great care and make sure that the main root is in a vertical position.

Dicogamy of these plants should be considered, especially for production purposes. In this case, cross pollination is necessary as the flowers are partially self-incompatible. Therefore, it is good to plant different cultivars during sowing.

Macadamia planting can be done through seed. The seeds maintain a very low viability, therefore, the sowing should be done as soon as the fruit is collected during the fall.

One way to speed up the germination process is to file the hard shell that protects the embryo, or to shell it, taking care not to mistreat the embryo.

Certainly, the hardness of the shell is a factor that can affect germination. For this reason, it is recommended to look for these species in nurseries where they have already been grafted to ensure the success of the first phases of macadamia growth.

Aerial view of a Macadamia plantation in South Africa. Source: LBM1948

Graft

This option can be done eight months after transplanting the germinated seeds to the bags, as long as they are already 40 cm high and 0.5 to 1 cm thick. The technique used is the lateral veneer graft.

Later, mature branches are taken from healthy trees with a diameter approximate to that of the pattern and that are at least 10 cm long and have three nodes.

The branches from which the quills are obtained must be ringed about eight weeks before to produce the accumulation of carbohydrates and in this way promote the growth of the lateral buds.

The graft must be tied with plastic tape and the base of the graft must be covered with a solution of 95% paraffin, and 5% beeswax in order to avoid drying and subsequent damage to the graft.

The grafts are ready to be taken to the field once they present two shoots of 30 cm in height approximately three months after the process carried out. Immediately they are transplanted, the plastic tape of the graft must be removed, but it must be kept so that the origin of the tree can be identified in the plantation.

Pruning

Pruning is very important during tree formation, because its branches are weak and can easily break due to the action of the wind. Therefore, pruning should be aimed at avoiding the formation of Y-shaped branches on the tree.

Harvest

Harvesting of macadamia nuts is done on the ground. Nuts should never be picked before they fall naturally from the tree, as only then have they reached maturity.

Macadamia nuts are harvested once they fall to the ground. Source: Forest & Kim Starr

Diseases

Maya (

It is a disease that occurs frequently in lands that contain decomposing organic matter and that have poor drainage. It is recognized by the presence of reddish leaves that fall very easily, and because the roots or damaged areas produce a fermented smell.

Root rot (

This disease is common in clay soils with poor drainage. Similar to the symptoms of maya, it is recognized by the development of reddish leaves on the tree, but in this case they do not come off even when the tree dies.

On the other hand, its presence is recognized in the bark and wood at ground level because it has a light brown color, and when it is removed, a white mycelium developed in the shape of a fan is observed.

Other diseases that can be found in macadamia are leaf burn, flower blight, stem canker and black root rot, fungi such as Gloeosporium sp., Macrophoma macadamiae, and some nematodes.

Pests

Bee drag (

It is an insect that stops the growth of the plant because it feeds on the new leaves or shoots. It can be treated by using pigeon peas that are efficient at capturing this hymenoptera.

In addition to this, it is advisable to destroy the nests of this bee that are 200 m around the plantation or the area where the damage was achieved.

Ant (

The ants cut the leaves or completely defoliate the trees, negatively affecting their growth. It is difficult to treat, but it is recommended to distribute recommended products against ants along all the paths of the plantation and even more so around the ant hills found.

Nut borer (

It is a larva that pierces the fruits and forms galleries between them and the shells. After piercing the shell, it feeds on the nuts and leaves a hole through which opportunistic fungi can enter.

Damaged walnuts are easily identified as those that have been affected by this insect show the excrement of the larva, which has a sawdust appearance.

Because this pest attacks fruits, it cannot be treated with chemical insecticides, but biological controllers or insecticides are being tested to combat this larvae.

Other pests that affect macadamias are aphids, mites, and rodents such as rats and squirrels.

References

1. Duke, JA 1983. Macadamia integrifolia Maiden & Betche, Macadamia tetraphylla L. Johnson. Taken from: hort.purdue.edu
2. The Taxonomicon. (2004-2019). Taxon: Genus Macadamia F. Von Mueller (1858). Taken from: taxonomicon.taxonomy.nl
3. Healthy food. 2017. Benefits of Macadamia. Taken from: Alimentossaludables.mercola.com
4. Agromatic. 2019. Macadamia cultivation. Taken from: agromatica.es
5. Virtual science library. 2017. Macadamia. Taken from: web.archive.org
6. Encyclopaedia Britannica. 2019. Genus Macadamia. Taken from: britannica.com