Background Essay: Floral Arrangements
In order to reproduce, most plants have to produce seeds, the equivalent of fertilized embryos in the animal world. To produce seeds, plants must fertilize their eggs with pollen - optimally with pollen from another plant of the same species rather than pollen from their own flowers. Plants have evolved many strategies that improve their chances of successful pollination.
One of the most common pollination strategies uses the wind to disperse pollen. This method can be effective, especially where a population of a particular species is dense. The lower the density of a population, the lower the odds that any one pollen grain will fertilize the egg of another plant. This is why many plants produce huge amounts of pollen. In such cases, the energetic cost of producing a lot of pollen, even if much of it will go to waste, is offset by the improved odds of successful pollination.
Another common pollination strategy uses animals, especially insects, to collect and transfer pollen from flower to flower. Most plants that have evolved this strategy use brightly colored flowers and energy-rich nectar to lure bees, butterflies, and birds to their pollen-producing parts. As the creatures sip nectar they unwittingly pick up grains of pollen on their feet and bodies, which they will carry with them as they move on to other flowers.
One of the most elaborate pollination strategies involves luring insects to flowers with the false promise of food or, in some cases, sex. The Australian hammer orchid, for example, takes advantage of a mating ritual of the Thynnid wasp, in which the female wasp waits on top of a branch or plant for a male to spot her. The hammer orchid's flower mimics the female wasp, complete with a fake shiny head and furry body. The orchid even releases a chemical similar to the pheromone that female Thynnids use to entice males. When the male wasp tries to mate with the dummy female, he becomes covered in pollen instead. He flies away, only to be fooled again by another orchid pulling the same trick. In the process, the wasp transfers pollen from flower to flower.
Interestingly, orchids, known more for their beauty than their bag of tricks, specialize in this strategy. As many as 10,000 species of orchids - some offering enticing scents, some offering mate look-alikes - use deception to achieve pollination.