Tuesday, April 3, 2012

Evolution of Flight

What a wonderful innovation it was when plants learned to fly. Plants? Flying? The ancestors of plants left the water about 350 million years ago during the Devonian. They were accustomed to hanging out in or near the water and the first plants were probably pretty soggy. For the most part mosses, which are most similar to the ancestral plants, also like moist environments. They reproduce by sperm, which are carried by raindrops to a nearby egg. Mosses are pretty but they don't fly.


Magical Understory at Yoho

Moss Clump

But almost simultaneously with the emergence of mosses, genera like Selaginella came into their own. Selaginella plants sent their spores flying into the air, perhaps the first instance of a flying plant, or at least part of one. A modern-day example of Selaginella is the common ground pine of northeastern woodlands. Before the flash bulb was invented, the copious spores of ground pine were ignited to produce a burst of light for old time photographers, a great example of plants in the service of art.

The ability to travel by air must have provided a profound selective advantage for plants that could do it. Spores, pollen, and later seeds could disperse in every direction, landing in new habitats and colonizing them.


Pine strobilus

Quercus catkins

Developing pistilate flowers

Some plants, for example grasses, reproduce exclusively through the agency of wind. A month on the Canadian prairie showed me how well grasses were suited to a windy environment.

I imagine that wind pollination had some drawbacks though. For example, since dispersal is random it means that the plant has to produce many more seeds or pollen grains than will survive. My guess is that the benefits far outweigh the drawbacks. The plasticity of plants, whether we think of it in terms of their ability to fly or their ability to evolve into new habitats, is one of the most amazing things I can imagine.

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