Tuesday, 20 August 2013

Orchids up to their tricks again

The duplicity of orchids is well documented. Bees, for example, are tricked by orchids that disguise themselves as the brightly coloured flowers of neighbouring plants.

However, researchers have noted a new twist to this botanical decpetion. The Oncidiinae group of orchids is one of the most diverse groups of flowering plant in the world, with around 1700 different species being found across South and Central America.

What is intriguing is that most of them are able to attract pollinators without rewarding them with the valuable oil or nectar which they receive from other flowers.

In the plant world, successful fertilisation involves attracting pollinators, such as bees, to transfer pollen from one flower to another, usually in return for a reward.

Researchers from Imperial College London and Kew Gardens have noted that a specific orchid, the Trichocentrum ascendens from South America, of the Oncidiinae group, does not do this.

In a ten-year study published in the journal Proceedings of the Royal Society B, they report that the Trichocentrum tricks pollinators by closely mimicking the colour and flower shape of another plant family, the Malpighiaceae, whose flowers produce a plentiful supply of oil.

Vincent Savolainen, Professor of Organismic Biology in Imperial's Department of Life Sciences, explains: "These reward-giving flowers have evolved a very special colour called bee-UV-green, that is highly distinguishable to bees' sensitive eyes. The Trichocentrum ascendens and other Oncidiinae orchids copy the special colour so precisely that bees are unable to distinguish between the flowers, visiting an orchid and pollinating them without the reward they may expect."

It could be that not producing nectar means the sneaky orchid can divert more energy to growing strong and producing more successful future generations.

Caption: Stigmaphyllon sp. (centre; Malpighiaceae) and Oncidiinae orchids Trichocentrum ascendens and Rossioglossum ampliatum (left and right; Oncidiinae: Orchidaceae)

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