Along the Air Line... Pollination Strategies
The Air Line Trail in Eastern Connecticut - Stan Malcolm Photos

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Put pollen from a grass and a daisy under a microscope and the differences jump out at you. The grass pollen will be small, angular, and textured; the daisy pollen will be large, round, and relatively smooth.

Generalizing, grass pollen is typical of plants that disperse their pollen on a breeze. It is light and has a surface meant to catch the air and fly. Daisy pollen is typical of plants that use insects to disperse their pollen. Their pollen is heavy, often sticky, and - relatively speaking - drops like a stone if shaken loose from the flowers. If you keep a vase of daisies in your home, look for the pollen to settle on the table below.

Daisy

Grass

To determine if a plant uses wind or insects as its pollination strategy, you don't have to look at the pollen, just look at the flowers. Typically, wind pollinated plants have inconspicuous green or brown flowers while insect pollinated plants include all the showy varieties we so enjoy.

Goldenrod, one of the true beauties of summer, suffers from the bad rap of being thought to be the source of allergies. A glance at the showy flowers ought to be enough to dispell the myth, but it persists. The true culprit is ragweed, a green-flowered plant that blooms at roughly the same time - and disperses its pollen on the wind.

Goldenrod

Ragweed

Plants and insects have struck a bargain through co-evolution. Plants produce nectar as a reward for pollination services. Insects receive the nectar, and sometimes a share of the pollen itself - as in the case of bees and beetles. Flowers typically produce far more pollen than is necessary for fertilization so they can afford to share.

Among the insect pollinated plants, we can use flower anatomy to make good guesses about the type of insect relied upon. While the rules are not perfect, they're right more often than not.

Azalea

White flowers, especially those like azalea or bindweed with deep pockets, slender tubes, or "spurs" holding nectar, are often moth pollinated. The white color improves night visibility and the pockets require a moth's long proboscis to reach the nectar - at the same time assuring that the moth's head and body are liberally sprinkled with pollen.

Similarly, brightly colored (often non-white) flowers with long spurs such as touch-me-not (jewel weed) may be pollinated by day-flying butterflies - again because it takes a butterfly's proboscis to reach the nectar. But some insects, notably beetles and bees, will cheat by chewing a hole in the side of the flower, bypassing the stamens and pistil - the plants reproductive organs - and getting directly to the sweets. Of course butterflies can exploit all sorts of flowers, not just those with deep reservoirs of nectar. They do just fine on daisies where the pollen is essentially laid out on a plate: the composite cluster of yellow disk flowers.

Beardtongue - and other members of the Scrophulariaceae and Labiatae (Mint) families, among others - have cylindrical flowers designed to allow pollinators to enter, being "doinked" with the pollen in the process. Here the typical pollinator might be a bumble bee.

Beardtongue

Milkweed has a similar strategy. Its pollen is massed in structures called pollinia. When a butterfly steps on a flower, a pollinium is attached - literally glued to a foot or tongue - only to be released when the butterfly steps on another flower and the pollinium sticks to the pistil.

Milkweed

Mountain laurel varies the theme once again. The tips of its stamens are captured under tension in pockets of the petals - traps ready to be sprung. When an insect lands on the flower, the petals are bent enough to release the stamens - and the pollen masses are slammed into the insect's body.

Dark red flowers often have a nasty odor. The point is to mimic carrion and attract flies as pollinators.

Of course insects and wind are not the only pollination mechanisms. Birds (e.g., hummingbirds) and bats have roles to play.

The next time you take a walk on the trail, try looking differently at the flowers you pass. How are they shaped? Can you find the pollen? Can you identify structures designed to hold nectar? Can you observe pollinators at work?