| General Description | The size of the crown can reach a length of up to 13 m. The crown is always covered by many branches full of leaves, making it a perfect shade tree, however there are some factors to take in to account; it has a superficial root system that makes it susceptible to falling during storms. It still can be used for shade, but crown cleaning is necessary in order to reduce wind retention. |
| ID Characteristic | Short cylindrical trunk. Whitish grey coloured, free of branches in the first meter of height, with fully circulated diagonal to horizontal branches that develop 4 leaves per whorl. Forms a rounded upright shape with dark green foliage, with elongated, pointy, serrated leaves, with an oblong shape and pointy end 7-25 cm large by 3 cm wide. |
| Shape | Macadamia tetraphylla is a round, upright shape tree, but different cultivars differ in shape. For example, the Macai Cultivar spreads an umbrella shape, and the kau cultivar spreads a broad-upright shape. The Macadamia Nut tree has a central trunk up to the first meter, starting to develop several branches spreading a canopy between 8 to 13 m. |
| Landscape | The Macadamia Nut tree is a good alternative for reforesting deprived areas and restoring biodiversity; not to mention the several extra benefits like preventing landslides, floods, and drought. The Macadamia Nut tree has a high economic value due to the rich and flavourful nuts that had been used for several purposes. |
| Propagation | Macadamia tetraphylla tree can be propagated through both sexual and asexual means. Sexual propagation by seed requires about 30 to 90 days before germination. This kind of propagation takes between 8 to 12 years to start producing fruits. As a result, asexual propagation has become very popular for Macadamia Nut tree propagation. The most common method of asexual propagation is grafting through whip grafting or side grafting, however whip grafting has presented better results. The propagation has to be done when temperatures are between 15 to 20 °C in order to succeed (spring or autumn). Air-layering is another asexual method that has been used, but it takes some time for the specimen to develop a root system. Plants need to be transplanted to well drained soil, with distances between 4 to 8 m within rows, with 7 to 11 m between rows. Grafted plants will begin to produce fruits between 4 to 5 years after being transplanted, producing between 3 to 4 times more than sexually propagated trees. |
| Cultivation | Macadamia tetraphylla was discovered in Queensland, Australia, which has an average elevation of 111 masl; however, Macadamia Nut trees grow at altitudes between sea level and 2000 masl. Altitudes between 700 and 1500 masl are a more suitable environment. Prefers well-drained soils that originate from volcanic material (andisols). The ideal pH for Macadamia is between 5.0 to 6.5. It has annual precipitation requirements between 1500 to 3000 mm. Macadamia thrives with temperatures around +15 to +25 °C, although will be able to survive in temperatures of +3 °C. Temperatures above +32 °C cause the tree to suffer from flower abortion. |
| Pests | There are some notable pests and diseases that are problematic for Macadamia Nut trees. Fungal diseases can occur, since the macadamia nut tree thrives in a rainforest environment surrounded by ideal temperatures and bushy foliage. Pruning is necessary to help with air circulation. The most common fungi are Anthracnose (Colletotrichum gloeosporioides), Husk Spot (Pseudocercospora macadamiae), and Raceme Blight (Botrytis cinerea). There are only two significant pests that affect the tree; Macadamia Nut Borer (Cryptophlebia ombrodelta), and Tropical Nut Borer (Hypothenemus obscurus). Both pests have natural enemies, such as native parasitic wasps and flies. |
| Notable Specimens | Brisbane Botanic Garden, Queensland, Australia. |
| Habitat | It is a native tree from the north east cost of Australia, specifically Queensland, Australia. It has an average altitude of 111 meters above sea level. It thrives perfectly with annual precipitations around 1500 to 3000 mm. In terms of soil, it prefers well-drained soils from volcanic origin (Andosol), and pH between 5.0 to 5.6. Macadamia tetraphylla grows directly from the seed, and takes between 8 to 12 years to start producing new fruits. |
| Bark/Stem Description | Short cylindrical trunk with a smooth, whitish grey bark. The main stem typically only rises to the first meter of height, before spreading several diagonal to horizontal branches. The main stem can reach between 0.20 to 0.70 m in diameter. The secondary branches can reach between 10 to 30 cm in diameter. The tree usually does not change its shape throughout its life. |
| Flower/Leaf Bud Description | Flowers grow in long racemes about 20 to 30 cm long; each flower is between 5 to 10 mm. The leaf is oblong with pointy serrated margins. Leaves measure between 7 to 25 cm. The leaf bud is tiny (2 mm), and round shaped with a small pointy side. |
| Leaf Description | Whorled leaf arrangement are formed by 4 leaves that are sessile (directly attached to branches, no petiole), with a dark green elongated pointy serrated margin leaf. They are a reddish colour when young. They have an oblong shape and pointy end. They are 7-25 cm by 3 cm with pinnate leaf venation. |
| Flower Description | The flowers grow in between the leaf whorls in long pendulous inflorescences or racemes 20 to 30 cm long. Each stalk holds between 100 to 300 hermaphrodite cream to pinkish coloured flowers. The Macadamia Nut flowers have been catalogued as apetalous flowers, or petaloid flowers, meaning that they don’t have petals. The flowers are 5 to 15 mm long. |
| Fruit Description | Macadamia tetraphylla is also known as the Rough-Shelled Macadamia because of its fruit features. M. tetraphylla has a drupe fruit that has a round shape between 2 to 3.5 cm in diameter with a pointy end. The fruit is covered by a shiny husk that contains one seed protected by a woody endocarp described as the hardest of all nuts. Non-smooth rough appearance. |