Obesus rotundus

The puffball tree is considered a keystone species on Pandora. It plays a critically important role in maintaining the stability of the environment. The globular balls produced at the tops of the trees and ends of the branches act as sponges, absorbing toxic gas from the atmosphere. This function is similar to that of the plant vacuole at the cellular level, which sequesters plant waste products and other molecules such as pigments and minerals. (Read more)
Although not generally a dangerous tree, Na'vi have learned to be wary of the gas balls, which can explode unexpectedly. The explosion creates a wide dispersal area for the tree's seeds.

The puffball tree also takes up naturally occurring sodium from the soil, much of which is extruded onto the surface of the leaves. The Na’vi collect the leaves to use the salt in their diets. Humans on Pandora discovered this important function of the puffball tree and returned samples to Earth to study its potential use in areas where overfarming and runoff has resulted in salty, unusable soil. Research is ongoing.