Botany

Trees of Australia Macadamia Tree



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The macadamia tree is an Australian native but there are now few left in the wild.  Luckily they are cultivated by the score for the commercial value of their nuts which can be eaten raw or roasted or used in cooking. Macadamia oil is the most mono-unsaturated oil available. The nuts are also high in fibre, selenium and phytic acid.

However, regardless of the allure of a delicious nut crop each year, macadamia trees make eye-catching ornamental evergreens with glossy, dark green foliage.

The macadamia belongs to the Proteaceae family and the Grevillea tribe which includes some Australian natives. Many species of macadamia exist but the two most used to produce edible nuts are Macadamia integrifolia and M.tetraphylla.

M.integrifolia is regarded as the better type for several reasons:

*  Research, selection work and breeding programs have concentrated on M.integrifolia
*  A higher sugar content means the kernels brown better when roasted.
*  M.integrifolia is more resistant to water stress and performs better in warmer conditions.

The macadamia is native to the subtropical rainforests of the east coast of Australia, occurring between latitudes 25o to 31o south, with M.integrifolia occurring mainly in the northern half of the range.

M.integrifolia can be differentiated by:
*  having three leaves per whorl as opposed to four per whorl of M.tetraphylla.
*  having a less spiky leaf
*  having (mostly) white flowers as opposed to (often) pink
*  generally smooth nut and seed surfaces rather than rough or pebbled as is M.tetraphylla.

M.integrifolia (tree) is roundish in shape with a height and spread of around 20 metres, averaging 12 to 15 metres. The tree develops a tap root with a supporting structure of lateral roots. The leaves vary in length from 75 to 225mm. New growth is pale green but the tips may be a light violet. The flowers have a sweet perfume and are borne on long sprays (racemes) which hang from the axils of the leaves. Mature racemes may be 100 to 300mm in length and bear 100 to 300 flowers. Around 10% of the flowers will develop into nuts.

When mature, the fruit measures about 25mm in diameter. A bright green covering or pericarp cover the brown nut which itself has an outer, hard shell and an inner creamy kernel. In the wild, flowers, immature and mature nuts grow simultaneously. Nuts fall to the ground between March and September.

Propagation is usually through cutting and grafting. Viable harvests can be expected when trees are about ten years old providing they have had favourable conditions and good management during their formative years. The macadamia nut is so hard that there are few animals or birds which cause much damage to the crop.

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