A grove of aspens can be one tree

Quaking aspen spreads by roots that send up new trunks. A stand of thousands of stems, covering hectares, can be a single genetic individual. The famous one in Utah is a forest you can walk through, and it is one plant.

Aspen reproduces by seed and, far more successfully in much of its range, by clone. A root runs, a shoot comes up, and the shoot is the same genetic individual as the trunk it left. Over time the shoots become a grove, flower in synchrony, turn the same colour in the same week, and share a fate if a disease finds them. Pando, in the Fishlake National Forest in Utah, is the stand people travel to see: on the order of forty hectares, tens of thousands of trunks, one set of genes, one connected root system. Other clones are smaller and more ordinary. The ordinary fact is the strange one. A forest can be an organ.

The age is the part to hold lightly. A clone has no single set of growth rings. The trunks above ground are young. The root that joined them may be thousands of years old, and some estimates say much older. The estimates disagree, and they should be allowed to. What a genetic test does not disagree about is the identity. Walk through Pando and you are walking through one plant, the way you walk through the crown of an oak, except the crown has been planted in the ground at intervals and each planting has a trunk. The largest fungus is another entry. This is the version you can get lost in, and still be inside a single organism.