Thursday, 26 July 2007

Not showy but still a spectacle

Quite deservedly, orchids have a reputation of being showy plants. However, there are several species of orchid that rather let the side down and it was one these that I encountered just the other weekend. In a damp and heavily shaded corner of a Suffolk wood I was shown 16 brittle-looking flowering stalks. These belonged to a small colony of bird’s nest orchid, a species more commonly encountered in the beech woods of southern England. To be honest, the flowering stems looked liked long dead plants but a closer inspection revealed that they were alive. Pale brown in colour, each of the individual flowers that made up the inflorescence was characteristically shaped. The sepals and petals formed an open hood at the top of the flower, while a double lip extended down below, the whole effect strongly reminiscent of common twayblade (a more common and related orchid species).

The flowering spike represents the culmination of the plant’s hard work, acquiring sufficient nutrient reserves below ground to produce and push up a stem; bearing flowers that would be pollinated by visiting insects. This process may take a decade of work, with the plant deriving these nutrients through a rather unusual association with a fungus. The bird’s nest orchid has virtually no chlorophyll and so is effectively unable to carry out photosynthesis, the process so central to most plants. Instead, the orchid gets its nutrients by devouring its living fungus partner which, in turn, obtains its carbohydrates through a symbiotic association with tree roots. In essence, the orchid has cut into a partnership between the tree and the fungus, exploiting both partners to its own advantage. The importance of the fungus is such that seeds produced by the orchid will only germinate where this particular fungus is present and this may be why these orchids are found in clumps within particular parts of a wood.

The English name of the orchid, and also its Latin, is a reference to the appearance of the root system. Each plant has a rhizome around which a tangle of roots radiate out in an untidy manner. This looks very similar to the untidy stick nests built by pigeons and doves. The preference for moist (though not waterlogged) ground within shaded woodland may be one of the reasons why this orchid has declined so dramatically across its historical range. There are just a handful of sites within East Anglia where this plant may be found and so, given the plant’s appearance, it is probably best to visit a known site rather than try and find one yourself. Despite growing up alongside the southern beechwoods, where this species is more common, it remains a spectacle well worth seeing.

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