From the New Zealand Native Orchid Journal #64:

One thing that surprises us about European orchids is the complexity of their labella, for these are mostly insect-pollinated species. The often-quoted words about labella, "variously modified and decorated to insect pollinators" really means something in this insect-rich countryside.
There are two species of butterfly orchids in Britain - Platanthera chlorantha (the greater butterfly orchid) and P. bifolia (the lesser). They are common throughout the temperate regions of Europe, and there are on species on the mainland.


There is no clear distinction on size or habitat or flowering season. Each is 20-60cm tall, with oval shiny green basal leaves, and a few stem bracts. The stem bears 10-25 white flowers. The lateral sepals are long and somewhat pointed, sticking out and down; the dorsal sepal and upper two petals from the hood. The labellum points straight down, and is strap-shaped but with a long tubular pouch (the spur) at its base; the entrance to the spur is clearly visible from in front of the flower, and through its semitransparent walls a pool of nectar is often visible. The flowers are powerfully scented, more so at night; they attract night-flying moths, whose long proboscises can probe down into the spur to reach the nectar reward.
The thing that distinguishes the two British species is the position of the pollinia. Those of P. chlorantha are widely separated at the top of the column on either side of the entrance to the labellar spur, and each is attached to a large viscidium. The moth's broad head detaches the pollinia, which stick to the sides of the head, often almost covering the eyes. The pollinia of P. bifolia, on the other hand, are close together, and attach to the moth's proboscis. In both cases the contraction of the stalks of the pollinia cause them to point forward so that they brush against the centrally-placed stigma of the next flower visited.