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. […] The sum of all the stems, roots, and leaves of one such individual is called a clone. Quaking aspen clones may spread far across a landscape as they continue to reproduce vegetatively. How far one clone can migrate depends on how long it can live.

And how long might that be? The short answer is that we don’t know. It might seem as if all one has to do is count the annual growth rings in the individual stems. Aspen stems that I’ve studied in the Colorado Front Range rarely exceed 75 years. Elsewhere individual stems occasionally reach 200 years. But the age of individual stems tells us almost nothing about the age of the clone they belong to, since its living stems may only be the latest to sprout. The oldest clone with a firm age is an 11,700-year-old creosote bush (researchers were able to date it by measuring the rate at which its circle expands). But aspens may actually be far older. Based on evidence such as the resemblance of some aspen clone leaves to fossilized ones, Burton Barnes of the University of Michigan has suggested that aspen clones in the western United States may reach the age of a million years or more.

For reference, a million-year old aspen organism would be four or five times older than homo sapiens.

No matter how awesome you think the universe is, it’s awesomer.