Christopher Plover says, "about the trees of Fillory. You see, there are many, but in truth, only one. ... The roots of the trees of Fillory intertwine, such that they become one." Quaking aspen trees are like this: they grow in clonal colonies which appear to be individual trees, but all the trees are genetically identical clones growing from a single shared root system, so each clonal colony is considered to be a single organism. One, called Pando, is the heaviest and oldest known living thing, estimated to be around 80,000 years old.