Most successful plant in the world

People call universities to find things out that aren't easily looked up, and for many years all the weird plant related questions have been forwarded to me. I'd like to think it was because of my success at answering such questions, as opposed my being weird. So it was not a surprise when my phone rang recently and someone wanted to know, for an article they were writing, what was the most successful plant in the world?

Now that's an interesting question because it can be answered from several different perspectives depending upon how you define success.

My first idea was that the most successful plant in the world was one of the domesticated grasses, a cereal grain. From its beginning as a wild middle eastern grass wheat has become the most commonly cultivated plant in the world. But rice provides the majority of calories to the majority of the world's people. And altogether cereal grains occupy something like 70% of all tillable land.

Now such plants are successful because they were useful and important to humans. Cereal grains have moved with us and native plant communities removed for the culture of these cereals, and in a manner of speaking cereal grains have become immensely successful. But without human intervention, they would not long persist in such vast areas.

And of course there are weeds. Weeds are adapted to disturbance, so they grow rapidly reproduce quickly, in great numbers, and then disperse widely. You probably didn't need to be told that, but now you know why. Nature produces disturbances, so weeds occur naturally to take advantage of these sites. But the thing that humans do best, and most frequently and thoroughly, is create disturbance, so weeds have greatly benefited by human activities. Agriculture can be defined as a systematic disturbance of natural communities for the purpose of growing domesticated plants and animals. So weeds have greatly prospered and gained great success as a result of human activities too, but they have done it on their own. No wonder such successful plants are so hard to eradicate.

Another concept of successful is longevity. Some aspen or sagebrush clones appear to be 10,000 years old, and that's a long time for one individual to exist. Some bristlecone pines are known to be over 7,000 years old. Such long-lived organisms are certainly successful. Osmunda cinnamomea, the cinnamon fern, certainly is a longevity contender too. 70 million year old fossils of this fern have been found that are virtually identical to the living species. This makes this fern the oldest known species, period, plant or otherwise. I have a fossil fern stem from the Carboniferous era over 300 million years ago that is anatomically identical with modern Osmunda ferns. So the group has been around for a long, long time. Selaginella, a clubmoss, is another genus with a very long history dating to the early Carboniferous, and that makes it the oldest living genus.

If you take a broad definition of plant, then perhaps a particular cyanobacterium (sometimes called blue-green algae), like this one pictured here on the right, might be considered the most successful and influential plant in the entire of Earth history. Sometime 2 to 2.5 or so billion years ago this cyanobacterium became a chloroplast giving rise to all of the other green organisms. When you look outside your window you see green because this incredibly tiny green cell, now functioning as a cellular component in all plants, has been duplicated in countless numbers. Cyanobacteria, including chloroplasts, are the only organisms that use water in photosynthesis for a hydrogen source, which leaves oxygen as a by-product. All of the oxygen that makes up 20% of Earth's atmosphere (and its ozone layer) is a by-product of photosynthesis. Talk about influential! This changed Earth history completely. Aerobic organisms such as ourselves were not possible until there was oxygen in the atmosphere. So in terms of sheer number, ubiquity, and influence, the cyanobacterium that became a chloroplast is probably the most successful green organism in the entire of Earth history. But we are probably wrong to call it a plant.

So there you have it. Depending upon the type of success you were looking for, those are the most successful plants.