One of the many lovely things we saw on a visit to my brother, who lives alongside the Crinan Canal in Scotland, was hosts of Greater butterfly-orchids along the canal banks near Carinbaan. As in many places this summer, strimming the verges of the tow path has been kept to a minimum and many plants are flourishing – there are swathes of Meadowsweet and Rosebay willowherb and far too may Common-spotted orchids, Dactylorhiza fuchsii, to count.
However the nicest surprise for me was to count no less than 45 tall, elegant spikes of Greater butterfly-orchid, Platanthera chlorantha on the stretch of canal path between Lochgilphead and Cairnbaan, without needing to get off my bike – I’m sure there were actually many more. The meadow where I usually see these in the Lake District only had a single flower spike this year but the weather on the west coast of Scotland must have suited them better and the reduced mowing regime is showing very clear benefits.
Greater butterfly-orchids differ from lesser ones (Platanthera bifolia) in having pollinia or pollen sacs which spread outwards from the tip to the base rather than lying parallel to one another along their length. The flowers are creamy white, tinged green, with a long, narrow lip and lobes which gives them a cross-shaped appearance. The really distinctive feature, and the clue to how they are pollinated, is the length of the nectar-filled spur behind each flower. Like a scaled-down version of Angraecum sesquipedale, which Charles Darwin famously used to predict the existence of a moth with a 35 cm long proboscis (Xanthopan morganii praedicta), this long spur suggests the orchid will only be pollinated by insects with a proboscis long enough to reach the nectar at the bottom. The flowers’ scent being strongest in the evening points to night-flying moths as the pollinators. Limiting the number of types of pollinators which can obtain nectar like this means that insects which collect the pollen are likely to visit other orchids of the same species, improving the chances of successful pollen transfer and cross-fertilisation.
In most orchids which use moths for pollination, the pollinia attach themselves to the insect’s proboscis and are then transferred to the next orchid the insect visits.
However, the position of the Greater butterfly-orchid pollinia means that they usually end up attached to the moth’s compound eyes instead and this proves to be an efficient mechanism of pollen transfer, with 70-90 % of flowers setting seed according to Harrap & Harrap’s Orchids of Britain and Ireland. Perhaps it’s no surprise that the population is thriving here, when given a little space and time. Great news for a species which has been lost from 46 % of its historical range in England and is classified as Near Threatened.