Compared with a mite or a virus, we humans are enormous. But we share this planet with other organisms that, in turn, dwarf us. At 100 feet, a blue whale is about 18 times longer than the average person; a giant sequoia, three times that. There are even larger giants on Earth, and you don’t have to travel to some far-flung corner of the world to see them. In 1992 two Michigan biologists startled the public by announcing their discovery of a fungus covering an area of 40 acres. Their announcement was soon followed by one from another group of researchers who claimed to have found a 1,500-acre fungus in Washington.
When I and two of my colleagues at the University of Colorado, Jeffry Mitton and Yan Linhart, first read about the fungi, we decided that the record had to be set straight. While the Washington fungus may in fact be the world’s largest organism in area, it is not the largest in mass. Its discoverers have yet to calculate its weight, but they do know that it probably weighs under 825,000 pounds--about double the weight of a blue whale but nowhere near that of a giant sequoia, which can tip the scales at 4.5 million pounds. Yet even the majestic giant sequoia is not the record holder. That honor goes to a tree that my co-workers and I have studied for years: the quaking aspen, a common tree that dapples many mountains of North America. Unlike giant sequoias, each of which is a genetically separate individual, a group of thousands of aspens can actually be a single organism, sharing a root system and a unique set of genes. We therefore recently nominated one particular aspen individual growing just south of the Wasatch Mountains of Utah as the most massive living organism in the world. We nicknamed it Pando, a Latin word meaning I spread. Made up of 47,000 tree trunks, each with an ordinary tree’s usual complement of leaves and branches, Pando covers 106 acres and, conservatively, weighs in excess of 13 million pounds, making it 15 times heavier than the Washington fungus and nearly 3 times heavier than the largest giant sequoia.
Pando reached such vast dimensions by a kind of growth, common to plants, known as vegetative reproduction. A plant sends out horizontal stems or roots, either above ground or below depending on the species, that travel some distance before taking root themselves and growing into new, connected plants. For us humans, who tend to view sexual reproduction as the only means of generating offspring, the method may seem a bit strange. Yet vegetative reproduction happens all around us. Every gardener witnesses it in one form or another. Strawberry plants, for example, send out stringy aboveground stems that can take root and form additional leafy clusters. Vegetative reproduction allows grass to produce lovely lawns (as well as foul language when it spreads into the garden plot). People who raise houseplants routinely take advantage of vegetative reproduction when they make cuttings of their favorite ivy or spider plant and root those pieces in new pots.
