Northern Ireland's Priority Species

Platanthera bifolia – lesser butterfly-orchid

 

Distribution map

Click here to view an interactive map of the Northern Ireland dataset as currently collated by CEDaR.
The map is generated through the NBN Gateway using their Interactive Mapping Tool.

 

Platanthera bifolia (L.) Rich.
Family: Orchidaceae

One of our most charming early summer wild flowers, Lesser Butterfly-orchid has a spike (compact or more lax) of up to 20 comparatively large cream or whitish-coloured, flowers that are sweetly scented in the evening. Each flower bears a very long slender spur at the rear. This orchid grows in a wide range of nutrient-poor, damp to wet, marshy or flushed, open habitats. They include unimproved pastures on acidic, heathy ground, the drier parts of peat bogs and open parts of scrub and woodlands. It also grows in calcareous fen and marsh habitats. In many places, but especially in southern and eastern Britain, colonies have rapidly shrunk and disappeared during the last 25 years.

In brief

  • While recorded as quite a widespread species throughout Britain and Ireland, it is most frequent in the west and north of these islands
  • Populations tend to be small and sometimes exist only fleetingly at particular sites
  • It flowers from May to July
  • Decline has been happening since about 1930, but has accelerated in the past 25 years, especially in England
  • A truly Eurasian species, it occurs throughout Europe from 70 N in Scandinavia southwards to the Mediterranean region, but is absent from southern parts of Spain and Greece

Species description
Usually between 15-25 cm tall, generally bearing between 12-20 cream or greenish-white, delicate-looking, scented flowers, although on occasions there may be as few as three to six flowers on a stem arising from two broad basal leaves. Narrow stem leaves 2-5, grade into the flower bracts which are as long as the ovaries. The twin pollen sacs are arranged upright and parallel inside the throat of the flower. The lower lip of the flower is strap-shaped and greenish towards the tip, and the very slender straight spur is 15-20 mm long. It appears in a wide variety of open, grazed or rough, damp to wet grassy sites, on both acid peat bog and heaths and on damp calcareous soils. Much more rarely it occurs on screes, scrub and on the margins or in openings in woods.

Life cycle
A tuberous perennial, the microscopically tiny seed germinates in spring, and after two years growth it develops a rooted shoot. In year three a tuber forms, bears a green shoot, and flowering may occur soon thereafter. The aerial parts are annual and do not persist.

Similar species
The closely related, rather similar Greater Butterfly-orchid, P. chlorantha (Custer) Reichenb., regularly shares sites with P. bifolia. It is the only similar species with which it could be confused. Greater Butterfly-orchid has brighter green leaves, both spur and lower lip (labellum) of the flower are longer, and the pollen sacs lean towards one another, rather than lie parallel. P. bifolia is more tolerant of acid conditions than P. chlorantha.

How to see this species
In Northern Ireland Lesser Butterfly-orchid is most frequent in the western uplands of Co Fermanagh where many sites have been recorded in recent years. As with other wild orchids, it is important to look for the plant when it is in flower, since otherwise it is almost invisible.

Current status
In Britain colony decline began about 1930, and there has been a loss of approximately 60% of all recorded sites since 1987. There have also been losses in Ireland, but not on so large or dramatic a scale. However, in Northern Ireland better recording has produced a considerable number of new sites in recent years, particularly in counties Fermanagh and Tyrone, making these areas something of a stronghold for this orchid.

Why is this species a priority in Northern Ireland?

  • This species has steeply declined in terms of the number of sites across the whole of the British Isles in the past quarter-century
  • In Northern Ireland losses have been predominantly noticed in eastern counties, where colonies at about half of the previously known sites have probably disappeared

Threats/Causes of decline
In lowland habitats it has been lost through the widespread intensification of agriculture. Features of this include the conversion of heathland to pastural agriculture, drainage of soils, increased use of agrochemicals (both herbicides and fertilizers), slurry spreading and woodland disturbance. Upland populations have also been lost due to increased grazing pressure and coniferous afforestation.

Conservation of this species

Current action

  • The plant is listed as a Northern Ireland Priority Species of Conservation concern and a Biodiversity Action Plan will be prepared
  • Many of the known sites are monitored on an ad hoc basis by field botanists

Proposed objectives/actions
The status of Lesser Butterfly-orchid will be surveyed and monitored and appropriate conservation action undertaken if required.

What you can do
You can assist by helping to monitor the health and size of populations. Any sites additional to those currently known would be of great interest. All records should be reported to either the Botanical Society of the British Isles (BSBI) or to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, Co. Down, BT18 0EU. Tel: 028 9039 5256, email: cedar.info@magni.org.uk.

Further information

Links
Online Atlas of the British and Irish Flora

BSBI distribution map for Lesser Butterfly-orchid

Flora of Northern Ireland - Lesser Butterfly-orchid

Irish Wildflowers

West Highland Flora

Literature
Foley, M. & Clarke, S. (2005). Orchids of the British Isles. Griffin Press in association with the Royal Botanic Garden, Edinburgh.
Harrap, A. & Harrap, S. (2005). Orchids of Britain and Ireland. A & C Black, London.
Curtis, T. & Thompson, R. (2009). The Orchids of Ireland. National Museums Northern Ireland, Belfast.

Text written by:
Ralph Forbes