Fungimonium giganteum

The octoshroom resembles a giant purple mushroom that grows as large as many plants on Pandora. This fungus is presumed to grow large in the low gravity and dense atmosphere of Pandora, although some botanists think its gigantism is due to irradiation by its underground exposure to radioactive oxides and isotopes of xenon. (Read more)
Most of the body of the octoshroom lives underground in the form of an extensive network of filaments called mycelia. Some of the mycelia penetrate plant roots and absorb carbohydrates while providing the plant with a greater supply of mineral nutrients. The octoshroom is able to absorb and break down nearly everything in the soil, including ammonia, methane, chlorine, various forms of nitrogen, and xenon. Closer study showed that the octoshroom is also a radiotrophic fungus that can use ionizing radiation as energy for growth. A similar type of fungus was discovered on Earth after the Chernobyl nuclear accident of 1986 but its metabolism was not fully understood until the giant octoshroom was discovered on Pandora and studied further.

Spores of the octoshroom will germinate and grow new filaments wherever they land. It is possible that the spores of the octoshroom have found their way to Earth via the ISV fleet, although no specimens have been discovered there yet. Study is underway to determine the efficacy of the mushrooms for pharmaceuticals and bioremediation.