Orchids of Australia

By Dr Noushka Reiter 5 December 2012
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Stunning, mysterious and diverse, Australia’s 1700 orchids are the jewels of our flowering plants.

WITH MORE THAN 100 genera of orchids in Australia – the majority of which are ground-living and found nowhere else – it is impossible to cover the diversity without the weight of a large book.

We have more than 1700 of the 25–30,000 species in the Orchidaceae family known globally, yet, regrettably, 25 per cent of orchid extinctions occur here. In part our species are vulnerable because they require symbiotic relationships with specific types of ‘mycorrhizal’ fungi to grow and germinate, and many are pollinated by a unique species of pollinator.

Unravelling one thread in these complex relationships can have disastrous results.

Varieties that stand out are the greenhoods, flowering in winter and trapping unsuspecting fungal gnats to pollinate them. Spider orchids are the showy and alluring sirens, using several means to attract their pollinators. Sun orchids have numerous flowers resembling lilies and open on sunny days. Duck orchids employ entirely sexual deception to attract their pollinators. Perhaps the most bizarre of all are the underground orchids – members of a cryptic group that live out their lives entirely below the soil surface.

Which orchid is which?

The term mycorrhizal simply means “fungus root”. These microscopic fungi are found within individual plant cells from which the orchids absorb their nutrients; these can be located in the roots or other parts of the orchids. The degree of dependence on the fungus varies, with most orchids having the ability to draw energy from sunlight via chlorophyll. However, some orchids (such as hyacinth orchids and underground orchids) have taken this relationship to a point where they no longer have chlorophyll and derive all their nutrients from their fungal partner.

There are many ways in which Australian orchids are pollinated, but the majority require a third-party insect pollinator to transfer pollen from one plant to another. Some provide a pollen or nectar food reward; others simply mimic food-rewarding plants but provide no treat.

One of the more interesting pollination syndromes in Australia is sexual deception. Male thynnine wasps are drawn in by pheromones, and then copulate with the flowers, thinking they are female wasps. This transmits pollen between plants. These relationships are very specific, with many individual species of orchid pollinated by individual species of wasp.

Source: Australian Geographic Sep – Oct 2012