Windmill Trees

27.3 light years from Earth, on the planet Newhope, which orbits the Sol-type star Chara in the Hunting Dogs constellation, there exists a strange plant species known to the locals as the windmill tree. About ten feet tall when mature, its interesting feature is the set of six radially spoked fronds attached to a central hub protruding from a cavity near the top of the tree's trunk. Wind forces cause the fronds to rotate, much like a windmill. Inside the trunk, a cartilaginous ligament is attached to the hub, which stretches and winds around the shaft as the fronds turn in one direction. When tight, rotation ceases, and the fronds, triggered by the tightening of the ligament, change their aspect (similar to a sailboat tacking), and rotation continues in the opposite direction. The cycle repeats continuously, as long as wind pressure exists.

Most locals maintain a copse of windmills. Some attach small, lightweight shells to the tips of the fronds to produce a soft, pleasant whistling.

The only living creature on Earth to have rotation characteristics is the lowly E. Coli bacterium, which uses a little rotor to crank its flagellum for motation. Detailed information from a Physics Today article can be found here.