Design in Australian plants—The Australian Greenhood Orchid
It’s small and lives inconspicuously among the grasses of swamplands and is pollinated by gnats.
Although the flowers are a dull non-eyecatching green, the engineering constructions by which it achieves its primary purpose of pollination are extremely impressive.
The flower is a homemaker’s delight. It has a welcome mat, a front door, a roof, some steps to the kitchen, an insect-proof exit and protective screen. All insects which enter it receive a compulsory tour in exchange for their services as they pollinate the flower.
As a gnat lands safely on the front mat of the Australian Bearded Greenhood Orchid (Pterostylis sp.), attracted by the delights of its nectar, its trip up the large hanging petal is assisted by a ladder (or bearded labellum). Once through the open door formed by the hood or roof of petals, it’s a short trip to the inside base of the flower to sip the ambrosian delights of the nectar.
However, the price for a quick sip is swiftly charged. As soon as the gnat is inside the hood, the ‘spring-loaded’ petal up which it walked, snaps shut! The guest is now a trapped prisoner. There is only one way out for the gnat—up the hallway and through the exit. This hallway is formed by the overlapping and now shut petals. As it moves towards the exit, it must now push past the pollen which sticks to the insect.
Now it can easily push its way up through the grid of fine hairs around the exit to fly away to freedom. However, if it attempts to fly back through the hole for a parting drink, it soon finds that the exit has “disappeared”, hidden beneath the overlapping petals. Even if it could get inside it would find that the fine hairs could no longer be pushed easily out of the way. The inspection of the flower house is a ‘one way trip’ only!
Free to fly away, the gnat finds itself covered with sticky pollen. No, it does not wait around the same orchid, for the flower stays shut for up to thirty minutes—long enough to test the patience of even the most long-suffering gnat. The Greenhood Orchid will never get its own pollen back. The gnat must visit another Greenhood and then proper cross-pollination will have been achieved. Just in case something goes wrong with that particular gnat, the Greenhood resets its spring-loaded petal after a time and all is ready for the next one way trip.
Such intricate pollination devices in orchids were no accident but instead indicate design.