Morx was a massive forest in ancient times, centered around a gigantic tree (probably the Frant's Tree). The grassy areas were covered with mushrooms, allowing monsters to train by interacting with the tree and the fungi. It is the first training area you use in Monster Rancher 3.
Since the continental divide, what's left of Morx has come to cover much of the northern part of Aurora Island. Some believe the island itself only survived because of the huge amount of anima stored in Frant's Tree.