Species of the Month - June 2012
Greater Butterfly Orchid & Lesser Butterfly Orchid
Platanthera chlorantha Plananthera bifolia
The flower has 3 sepals and 3 petals. The lower petal hangs down like a strap and the lower 2 sepals form the wings at the sides. The upper sepal and the upper 2 petals are folded together to form a hood at the top. Underneath this hood are the 2 pollinia. In the GBO, as the picture above shows, these pollinia are far apart at their lower ends, though they converge upwards. In the LBO the pollinia are parallel and close together all the way down. Once you know this difference, the species are easy to tell apart, provided they have fresh flowers. Plants that have not yet flowered or that have finished flowering cannot be reliably identified, but it's worth noting where they are and going back when they are in flower.
The two species are genetically almost identical and have only diverged in recent times to accommodate the behaviour of different moths. The GBO is pollinated by Noctuid moths which stick their whole heads in between the pollinia to get at the nectar. The pollinia then stick to the moths' eyes and are transferred to the next flower they visit. The LBO is pollinated by hawk moths who simply poke their long proboscis between the pollinia, which are close together to ensure that they stick to the proboscis when the moth leaves.
The two species have different habitat requirements. Both grow in open ground, but GBO prefers a richer, drier, more alkaline soil, such as roadside verges or hay meadows, while LBO will grow on poorer, wetter, acid soils, including heather moorland. Despite this, there is a remarkable tendency for the two species to be found close together. When you find one, look for the other in ground nearby that's a bit drier/wetter as appropriate. When counting a population, don't assume they're all the same kind!
LBO is classified as "Vulnerable" and is one of the most rapidly declining wild flowers in the British Isles (Harrap & Harrap 2009). Its stronghold is in N & W Scotland where there is still plenty of unimproved grassland and heath, but even here it is under threat due to changes in land use, including grazing levels.
GBO is classified as "Near Threatened" but is more widespread across Britain than LBO. Where it occurs on road verges they should be managed sympathetically for it. In some places it may be threatened by the spread of bracken.
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4 Jun: Jan Hamilton found a patch of a dozen LBO's at North Cuil.
9 Jun: Sallie and I saw LBO in Glengour on the Lochaber Biodiversity Day outing.
17 Jun: Jan found another patch of LBO's in a different place at North Cuil
19 Jun: Bob Groves found one LBO at Little Ganavan.
21 Jun: Jan found 7 GBO's at Duror
25 Jun: Bob found some GBO's at North Connel.
7 Jul: Gela found 2 GBO's at Kilchrenan
May 2012 - Small Copper