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Plant reproduction relies on interspecies relationships

Nature never ceases to amaze. Of particular interest are the many and specific relationships between plants and their pollinators, including methods of seed dispersal that plants employ.

For example, some species of hummingbirds have evolved special adaptations for collecting nectar from specific flowers, such as the tropical heliconias (herbs related to bananas). In turn, the flowers of these plants have evolved to accommodate specific species of hummingbirds. The unique shape of the plant's flower is of such a proportion so as to attract only one particular species of hummer.

If it wasn't for the hummingbirds' specially adapted bill, there would be no way for the bird to reach the flower's nectar and, ultimately, for pollination to occur. These incredible symbiotic relationships, found throughout the world, appear in many different organisms that range from simple to complex.

In one particular astonishing example, there is a plant that produces a flower so unlike that of any other that it doesn't even look like a flower. In fact, what it looks like is an insect. A species of wasp is its lone pollinator and, in order to attract this insect, the flower has evolved in such a way that, amazingly, it resembles the female counterpart of the wasp!

What's more, the flower's fragrance mimics the scent that the female wasp emits to attract a mate. Once the male of the species arrives at the plant, it attempts to mate with the imposter. Special flower-parts apply pollen grains to the male wasp as it struggles with the flower. Later, when the male wasp "mates" with another female facsimile, the pollen is transferred and, thus, the perpetuation of the species of plant is ensured.

In a local example, the federally endangered western prairie fringed orchid, located in scattered populations throughout wet prairies of the region, has evolved a unique relationship with an equally unique insect: the hawk moth (sometimes called Sphinx moth).

Several years ago I assisted the late Minnesota DNR plant ecologist Janet Boe in a search for the rare orchid on public land near Mentor, Minn. We found several of the beautiful plants that were a couple of weeks behind in blooming.

Normally, as she related to me, the plants should have been in full bloom and easily observable over the tops of prairie grasses, sedges and other forbs. Most of the orchids that we encountered were nearing blooming stage, and only a few were in full and glorious blossom.

Aside from the gem-like quality of the multi-headed plants and their beautiful flowers that resemble the body shape of angels, the plant has also evolved the unique aforementioned pollinating strategy with the hawk moth. Unlike most flowers that are pollinated during daylight hours, the western prairie fringed orchid is pollinated at night. But not just any pollinator will do.

The hawk moth, with its specially adapted long tongue, is the only insect that can probe the orchids' nectar caches. Furthermore, as the moth hovers and feeds on the nectar, two specialized pollen-bearing structures brush pollen grains onto the moth's properly spaced eyes.

As the moth feeds and visits other orchids, the pollen grains are transferred, the plants are fertilized and genetic diversity is the result. This is a classic story where one species' survival hinges on another. It is, without a doubt, a fragile and important relationship.

As fascinating as pollination is, other interesting attributes of plants have to do with seed dispersal. While some seeds are carried by the wind, other seeds, such as acorns, usually don't fall far from the trees that produce them. In the case of oak trees, animals are often the primary mode of seed transport.

It's probably no accident that acorns evolved to taste good. If it weren't for their palatability to many species of wildlife, oak trees might very well be less abundant than they are. Tree and ground squirrels, other rodents, such as mice and voles, deer and bear, as well as many species of birds like blue jay, wood duck, ruffed grouse and wild turkey, actively seek out acorns for food.

Seed dispersal is performed by oak trees like this: the blue jay picks up a fallen acorn from the ground or plucks one from a branch and flies to a better perch from which to break open the shell. In the process, the bird drops the acorn 100 feet from the tree where the acorn was found. Thus, if no other animal finds the blue jay's lost acorn, it will, perhaps, germinate and grow into another acorn-producing oak tree.

Other plants produce seeds that stick to the fur (or clothes!) of animals. The pesky burdock turns out clusters of seed-producing structures that readily adhere to just about everything that brushes up against them. This type of seed dispersal mechanism, which many other plants employ too, is very effective at transporting their seeds to distant places and habitats.

Indeed, we are lucky to live in a land of abundant wild places. Nature, and all its wonders, is all the reason we need to get out and enjoy the great outdoors.


Blane Klemek is the Bemidji area assistant wildlife manager, DNR Division of Fish & Wildlife. He can be reached at