Groveknot grows as round, dense balls of forked green stems, from the size of a head to the size of a cart wheel, hanging from the high branches. Its leaves are small, thick, and leathery, yellow-green, in pairs at every fork. In winter, when the great trees are bare, the balls stand out dark green against the grey crowns, and it bears clusters of translucent white berries full of a sticky, glue-like pulp. Where it roots, the branch swells into a burred, knotted lump of wood, the knot that gives it its name, and beyond a large knot the limb often thins and dies.

It lives on the old broad-leaved trees of the forest world, high in the crowns where birds rest, in both the uncut stands of the Elderweald and the trained trees of the Crownboughs. It is commonest on old, open-crowned trees and at sunny edges and clearings, rarer in the deepest shade.

Birds eat the berries and wipe the sticky seeds off their bills onto branches, where they root into the bark. A tree that carries one clump soon carries many. Groveknot takes water and sap but makes some of its own food in its green leaves, so it rarely kills a tree outright; it weakens it, and a weak tree loses limbs in the storms.

A seedling takes years to show, then grows slowly into a ball that may live as long as its branch. Cut back, it regrows from the knot; only cutting the limb below the knot removes it.

In the Crownboughs it is a pest of the halls: a knotted bough cannot be trained, a limb weakened by it can drop a gallery in a storm, and tending a hall includes cutting out every clump within reach and cutting below the knot. Shapers burn what they cut. The Wood Elves let it live and watch the trees it is on; a grove may prop a laden limb, or clear the ground beneath it, but it does not cut. The berries are poisonous to people, though birds thrive on them, and the leaves are a winter fodder for deer.

The argument is the forests' oldest in miniature. High Elves say a tender who will not prune is no tender, and point to the Elderweald’s broken limbs; Wood Elves say a tree that carries another life is doing what trees do, and that the Crownbough halls are not trees any more but houses. Wood Elves count groveknot as the tree’s guest, and a household under a laden tree speaks of having guests above. High Elf children are told that the knots are a tree’s grudges, and that a house that cannot cut its own grudges will be brought down by them.