Flax is mostly seen on grasslands, unless players harvest it to plant at their island, which is rare because flax has only 2 uses; it allows players to make rope instead of hemp or cotton and is used in Taming Gazelles and Ostriches. it provides two flax seeds and twine. Two twine allows the player to create rope.
Rarely do people use flax for rope, as hemp seems to be the more common method.