Helicoradian

The helicoradian (Na'vi name: loreyu meaning "beautiful spiral") is a zooplantae (part animal, part plant) possessing a single leaf that responds to touch by coiling up and retracting to the ground. Its neuromuscular system makes it difficult for xenobiologists to classify. Helicoradia can grow to 6-8 meters (20-26 feet) in height and 2.5 meters (8.2 feet) across.

Uses
The Na'vi use leaves of the helicoradian for ornate ceremonial robes as well as other garments, tents, and sacks. Orange pigments in leaves can be extracted and used for paint.

Defense Mechanism
The helicoradian is a type of "sensitive zooplantae" that responds to touch by coiling up so that the single large leaf is no longer exposed to any herbivores that would eat it. Because it grows in clusters, the touch response (possibly taxis) by one helicoradian often triggers the same response in others growing nearby so that the entire population recoils, one plant after another. This retraction is both defensive and an effective feeding mechanism to trap insects and small animals.

The Na'vi are able to wander among the helicoradian without triggering this defense response, but are warned of the presence of danger when the helicoradian starts to retract.

Commentary
When Jake Sully (in his avatar body) touched several helicoradia, the entire cluster retreated. It may have been, however, that the cluster was responding to the presence of a group of herbivorous hammerhead titanothere (which charged Jake in a territorial display).

Background
Helicoradia may have been based on Spirobranchus giganteus, which are small tube worms that can be found on the seas of Earth. These creatures do not only bear a resemblance, but also withdraw when disturbed.