The left-leaning red–black tree

The left-leaning red–black tree grows mostly on the Californian coast, in areas with Mediterranean climate. Its thin bark is a deep red, with streaks often approaching black. The leaves are bright green. It has been difficult to classify taxonomically, but botanists generally concur that it is of the same genus as the manzanitas.

It always leans left. If you stand to its south, it leans west; if you stand to its north, it leans east. The branches revolve to match your eyes. If two viewers stand on opposing sides, then the branches warp space, logically leaning two ways at once but perceptually, for each viewer, only in a single direction—a direction that differs according to the source of the gaze. You can see this in a set of photos at the Museum of Natural History, taken a decade ago by an ecologist at UC Santa Barbara, which show not just the same tree but the same view of that tree yet differ in their environmental backdrops. In each of these photos, the tree leans the same way with the same leaves and the same scrub jays in its branches—but the sea lies behind, for the camera pointed southward, or the mountains loom, for the camera pointed north.

Botanists, in attempts to understand this phenomenon, have tried holding a string between two viewers on opposite sides of a tree and observing its interactions with the branches, or placing a small child in the boughs and asking them to report whether their view of the world shifted as they revolved with the left-leaning branches that carried them. Results have been inconsistent. The string would sometimes meet no resistance, seemingly sliding through the tree, or suddenly break in two as it approached the wood. The child would say that they continued seeing the ocean even as they faced the mountains, or that they were indeed turning as the viewer moved, or that enormous birds with white wings had filled their vision, and the sea had erupted in flames.