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3 Oct 2017

Nuts about macadamias

 It is hard to miss a macadamia tree in flower. The Garden’s macadamia has exploded into flower this week and is giving off a strong perfume that many visitors have commented on.

As Australia’s only native food tree export, the sight of the abundant flowers raises hopes of an equally abundant macadamia nut haul. As any macadamia farmer will tell you, flowers do not always lead to fruit. The Garden’s single macadamia tree is yet to produce fruit, leaving our horticultural team curious about what might be missing from the nut-making equation.

One theory about the lack of fruit is that the tree may be self-incompatible. Most plant species prefer to cross pollen with other individuals to increase genetic diversity. Macadamias are known to prefer cross pollination so having one tree on its own is the most likely reason for the lack of nuts.

Macadamia trees are a pollinator’s dream with thousands of long, pale pink inflorescences covering every branch, each made up of hundreds of individual flowers. In its native Queensland and northern NSW rainforest habitat it is pollinated by native stingless Tetragonula spp. bees.

A group of tiny Tetragonula can be seen not far from the Garden’s tree, just outside of the Education classrooms, making honey in a spiral shaped hive. They hibernate over winter in Sydney and it’s possible that the macadamia’s early spring flowering is too early for the cold-phobic bees. Even if the Tetragonula are raiding flowers for pollen, some studies suggest that each inflorescence needs an incredible 150 insect visits for full pollination.

There are around six million macadamia trees in Australia worth an export value of more than $250 million each year. Macadamia farmers are very interested in how to boost pollination and increase the annual nut harvest so research will continue to focus on the intricacies of pollination services, as they’re referred to in the industry.
If you can visit the Garden over the next few weeks, make the macadamia a must see and keep your eye out for pollinators. You won’t be disappointed.

Don’t forget to thank bees next time you enjoy a macadamia nut. Now you know how much effort went into its creation.

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