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Floral Arrangements

Resource for Grades 6-12

Floral Arrangements

Media Type:
Video

Running Time: 3m 08s
Size: 4.4 MB

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Source: Oxford Scientific, Sexual Encounters of a Floral Kind


Resource Produced by:

WGBH Educational Foundation

Collection Developed by:

WGBH Educational Foundation

Collection Credits

Collection Funded by:

National Science Foundation

It's a problem faced by all seed-producing plants: how to get their pollen into the flower of another plant of the same species. This video segment from Sexual Encounters of a Floral Kind explores some of the strategies plants have evolved to solve the problem.

Alternate Media Available:

Floral Arrangements (Audio Description) (Video)

open Background Essay

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.

open Discussion Questions

  • The average hammer orchid blooms before the first female Thynnid wasps emerge -- timing that provides them with the undivided attention of the males. How do you think just precise timing could have evolved?
  • What other organisms can you think of that help pollinate plants? How does the structure of the flowers these creatures visit improve the chances of pollination? Likewise, how does the structure and behavior of the pollinator increase the likelihood of pollination?

  • open Transcript

    NARRATOR: In most cases, to reproduce, a plant needs to be fertilized by another plant of the same species. But, plants are literally rooted to the ground, so they must rely on other organisms or forces to spread their pollen.

    Flowers help this along. Flowers are attractive not just to humans, but to other organisms. Their color, shape and scent have evolved to attract pollinating go-betweens. Although many plants rely on the wind to disperse their pollen, others rely on insects...or birds...or even mammals.

    In Australia, the coral gum tree is fertilized by the acrobatic honey possum. With its agile body, the honey possum eats the tree's nectar. It uses its long snout and tongue to reach beyond the stamen, unwittingly collecting pollen on its fur and spreading it from one bloom to the next.

    Not all pollination strategies benefit the go-between. Bush fires in Western Australia make way for the hammer orchid, which looks and smells very much like the female thynnid wasp. Female thynnids don't have wings. They eat beetle larvae and spend most of their lives underground. They only surface to mate, perching atop plants and releasing a pheromone to attract a mate.

    But it's all in the timing. Several weeks before the female wasps emerge from underground, the hammer orchids bloom. Hammer orchids have evolved to mimic the appearance and scent of the female thynnid wasp. They rely solely on the male wasps for pollination (wasp buzzing).

    It is to their advantage to bloom before the female wasps emerge, lessening the competition for male wasps. When the male attempts to carry off his mate, the hammer motion ensures that the bundles of pollen are transferred from the orchid to the wasp's back.

    The next orchid he mistakes for a female wasp receives the pollen from the first. This time the hammer motion deposits the pollen onto the stigma and the second plant is fertilized.


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