Orchids in the Robertson Nature Reserve

The Robertson Nature Reserve does not have many species of Orchids growing in it, nor very beautiful ones, to be honest. But they are interesting, none the less.

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For an Orchid, rainforest can be a difficult environment, as light is the key factor, and the forest floor in a rainforest can be very dark indeed.

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One way to succeed in low light conditions is to do what the Potato Orchid (Gastrodia sesamoides) does. It grows without leaves, or chlorophyll, or even without feeder roots. According to the standard reference texts, this plant has tubers which are “invaded” by microscopic fungi and also bacteria, which together help the plant fix nitrogen, enabling it to live. I have found a reference tonight to a CSIRO paper which casts doubt on the supposed role of any bacteria. (I shall leave that debate to the experts.)

However, like the Hyacinth Orchid which I have discussed recently, this plant is also a “saprophyte”. The Potato Orchid lacks the attractive flowers of the Hyacinth Orchid.

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Another way to survive, as an Orchid in a rainforest, is to grow as an “epiphytic” plant, using trees as hosts, but not being parasitic upon them. In other words, just growing high in the branches of the trees, using them as a perch. This way, you can get all the light you need. Holding moisture is then the limiting problem.

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The charming Orange Blossom Orchid(Sarcochilus falcatus) grows with its thick roots buried in the Rock Felt Fern (Pyrrosia rupestris) which grows thickly upon old Blackwood trees (Acacia melanoxylon). These mats of fern roots act like sponges holding plenty of moisture for the Orchid’s roots.

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Photo of the Orange Blossom Orchid at left. It gets its name from its sweet perfume.

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The Dagger Orchid (Dockrillia pugioniformis) (formerly Dendrobium pugioniformis) is less showy, having tiny greenish flowers. It forms straggling masses of wiry roots which just hang from the branches of Sassafras and Coachwood trees. Apparently the roots are able to absorb enough moisture for the plants to survive.

 

This article by Denis J Wilson kindly reproduced from his The Nature of Robertson Website.

Updated 5th July 2016