Report of Professor Ian Denholm's talk to the Society on 27th March 2018

By Joyce Bunting

The wild orchids of Britain and Ireland

Dr Ian Denholm, Evolutionary Biologist and Ecologist at the University of Hertfordshire, explained that all orchids found growing wild in Britain and Ireland are terrestrial orchids, with roots which extract nutrients from the soil. Many orchids from the tropics are epiphytes: they live attached to trees but extract nutrients from rain water and air.

28,000 species of orchid are found worldwide – that is 2½ times as many as all bird species across the globe. They are a very diverse group - some with quirky names referring to their appearance. The man orchid for example, has lots of small flowers which have a superficial appearance to human form. Then there are monkey, frog, lizard, butterfly, lady’s slipper and bird’s nest orchids among the 52 species which grow in Britain and Ireland.

Photo:Early Purple orchid - Orchis macula

Early Purple orchid - Orchis macula

In Harpenden at Knott Wood, the Early Purple orchid blooms in mid-May. On Harpenden Common one clump of the Green Winged orchid may be found by those who know where to look. It first appeared in 2003, but does not flower every year. The nearest large colony is at Langley Meadow SSI, near Stevenage.

The Fly Orchid grows at a few sites in Hertfordshire, including Telegraph Hill near Pegsdon. It has a blue iridescent patch on the lower petal which resembles a bluebottle. This is one of the orchid family’s tricks to attract insect pollinators.

Appearance and pollination

An orchid flower has 3 petals and 3 sepals, but they are displayed in different ways according to species. Bee orchid flowers have evolved to look so much like that insect that a bee will try to copulate with the flower. During the process he gets a parcel of pollen attached to his head – which he passes on to the next flower he visits. The right species of bee doesn't occur in Britain or Ireland so Bee orchids are self-pollinated here.

Photo:Early spider orchid - Ophrys spegodes

Early spider orchid - Ophrys spegodes

The Early Spider orchid is quite a small plant with a flower that looks like the body of an orb spider, hence its name. It is pollinated by small solitary wasps and bees. The Late Spider orchid is much rarer, confined to a few sites in Kent where plants are protected by metal cages in certain places to prevent trampling or grazing.

The Ghost orchid is a strange plant lacking chlorophyll with ‘upside down’ flowers. It spreads secretly by mycelia underground and was considered extinct in 2005 but flowered in 2009. It is not spectacular but extremely rare, known to only a few enthusiasts. It grows in beech woods in the Chilterns. The chief threat to this plant is the chalk soil drying out.

Several factors threaten the welfare of orchids. One is visitor pressure caused by orchid enthusiasts themselves. The delicate rosettes of leaves are easily crushed and their specialised habitats unintentionally damaged.

Another is the difficulty of keeping a clear gene pool of species. The sudden appearance in Britain of orchids from abroad can threaten the purity of the native species. Seeds are like tiny dust and may blow across the Channel or travel on clothes or shoes from further afield. Only a tiny fraction ever germinate. Colour variations appear spontaneously – white variations, for example – but these are not considered new species. Orchids hybridise very easily but the hybrids are not usually fertile.

Grazing animals and slugs may damage the plants above ground. But excluding grazing animals can result in overgrowth of other, more rampant, plants which will smother the orchids. So some conservation groups allow sheep or cattle access to these special sites occasionally. Putting down slug pellets can actually entice slugs to the area and is not recommended.

Our native orchids are rare beauties treasured by enthusiasts and must be preserved for future generations. Many species are on the list of plants of greatest conservation importance in the UK and have complete legal protection from picking and uprooting, practices that led to substantial declines and losses in the past.

Further reading

Ian Denholm recommends two recently-published books for those who are interested in orchids. Both titles are easily available from major retailers, and both can be downloaded digitally from Amazon, if preferred.

Orchid Summer: in search of the wildest flowers of the British Isles by Jon Dunn, Bloomsbury Publications, 2018.

The Orchid Hunter: A young botanist's search for happiness by Leif Bersweden, published by Short Books Ltd., 2018. 

A note from Margaret Pratt

Ian Denholm took a party of 15 to see the Early Purple orchids in Knott Wood. There were two lovely patches, just at their best. The bluebells were in profusion, too, though just beginning to go over.  Afterwards, we repaired for refreshments at Rothamsted Restaurant in the Conference Centre, which is is open to the public every Monday to Friday for coffee, lunch and tea.

This page was added by Rosemary Ross on 19/10/2018.

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