Edanna is one of 5 Lesson Ages that Atrus wrote to help teach his sons, Sirrus and Achenar, how to write Ages. This Age, which is a single, massive tree over 400 feet tall, was written to illustrate the concepts of nature and the inter-dependence of elements of the environment.
Edanna's lesson phrase was nature encourages mutual dependence.
Edanna's tree has sometimes been described as "inverted", because its structures all grow inward from a massive hollow trunk, and almost all of the plant and animal life that lives there exists inside it, rather than outside. There are three different biomes within the tree, each at a different elevation within the tree: Deadwood Ridge, the Forest, and the Swamp.
This is the highest part of the tree. Plant life is much more scarce here, though sunlight is much more abundant. Wind whistles through the mostly barren bark, and water is scarce. A red-breasted grossamery has made a nest here at the pinnacle of the tree, and corkscrew cattails stretch between various levels of the Ridge. A lone quaffler fig and its water basins provide water for these cattails. An aurora blossom and fan palm grow on at the top-most curls of bark. Lens blossoms also hang from overhead strips of tree bark.
Deadwood Ridge is also where both of Edanna's J'nanin Linking Books are located. The first is openly accessible, but the second—intended to be used after completing the Age's lesson—is hidden in a small curve of the tree trunk which is only accessible from the grossamery's nest. A nearby pool of sap has hardened over Edanna's Narayani mandala, which is made from bent branches.
The Forest is a much greener place than Deadwood Ridge. It is densely populated with plants, and has the appearance of a rain forest in miniature. Much of the Forest is open to the Swamp below, with tongue ferns being the primary means of traversing the area. One of the corkscrew cattails found in Deadwood Ridge actually has its roots here in the Forest. Another quaffler fig provides shelter to an electra ray. Squees and the barnacle moss on which they feed are also native to this area of the tree. Saavedro constructed a trap which could be operated remotely to capture the squees, which he used for food and clothing over the years he spent trapped in Atrus' lesson Ages. A swing vine connects this one of these tongue ferns to a path into the lower portions of the forest.
One of Saavedro's experiments, a massive venus flytrap, hangs in the space between these two areas of the forest. The lower forest itself is illuminated partially by light reflected from a pair of lambent orchids, which hang from ingrown parts of the tree high above. The quaffler fig's roots terminate here in a large water basin, which also feeds a fan palm. Another aurora blossom can be found near the center of the tree in this area. Narrow paths formed from natural tree growths snake throughout this part of the Forest, making navigation a challenge. A second swing vine connects the lower Forest with the Swamp.
At the base of Edanna's tree is a murky, humid region full of shallow water and dimly illuminated. A jumping dragon provides access back to the lower Forest biome. Papillion moths can occasionally be found resting nearby.