Orchids of the British Isles - Twayblades Content from the guide to life, the universe and everything

Orchids of the British Isles - Twayblades

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In this entry we look at the genus Listera . There are two species present in the British Isles, their common name being Twayblade. They bear little resemblance to what you would think an orchid should look like. The flowers are tiny and insignificant, not brightly coloured or very attractive. The name Twayblade, probably comes from the Swedish word Tva Blad, meaning 'two leaves'.

Common Twayblade Listera ovata

It is quite possible that you have passed by one of these orchids while out walking in fields or on the edge of woodland and not given it a second glance. If you were to look closely, though, you would see it has the characteristic orchid flowers.

This orchid has two very large, broad, oval-shaped leaves at its base. They look very similar to plantain leaves, but without the deep ribbing. From the centre of the two leaves a tall, hairy flower spike emerges, which can grow up to 70cm in height and bear up to 100 small yellow-green flowers. The flowers come out from the main stem and sit on a bulbous green ovary. The upper petals form a hood, which sits over the long forked lip. Down the centre of this lip there is a narrow groove, which secretes nectar.

Many insects have been recorded pollinating this orchid including male Springtails Apteris abdominator, male ichneumon wasps Ichneumon insidious and male sawflies Tenthredo atra. Bees are also attracted to the nectar, but are too large to be able to pollinate the plant. The rostellum1 explodes on contact by an insect, gluing the pollen onto the insect's head.

This orchid is very slow growing and can take up to 15 years to mature and form seed. However, frequently this orchid reproduces from aerial shoots sent up from the rhizome beneath the ground. It's not uncommon to see several plants in a row, each at various stages of maturity.

This orchid is widely distributed throughout the British Isles. It grows in a wide range of habitats from, grassland to woodland, coastal dune slacks and limestone.

Lesser Twayblade Listera cordata

As its name suggests, this orchid is very much smaller than its cousin, the common twayblade. It has two similar leaves at the base, which are more rounded than the common twayblade, and they are far more glossy and apple green. The flower stem again comes out from the centre of the leaves. It is hairy and reaches 10cm in height, carrying up to 20 flowers. Although the flowers are exactly the same shape as the common twayblade, they do differ in colour. The hood is a bronze colour with a green tinge, and the outer petals are creamy white, with a hint of green. The forked lip is far more pronounced than the common twayblade; it starts off creamy white at the base, then turns deep bronze towards the tip of the forks. One of the strange things about this orchid is that the flower keeps its shape long after the seed has been shed.

This orchid is mostly confined to the north, with a few small pockets in Northumbria, Yorkshire, North Wales and Ireland. It grows in wet acidic conditions on moors and boggy areas. It is most commonly seen growing with sphagnum mosses under heather and bilberry bushes, although it has been recorded growing in dry moss under pine trees.

It is often pollinated by female gnats Sciara thomae and small flies. It can also pollinate itself and multiply vegetatively, like the common twayblade.

1The sterile third stigma of an orchid flower, situated between the stamens and fertile stigmas.

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