When worn, the players Stamina will regenerate slightly quicker. This is similar to the other Stamina regeneration items found throughout the game.
A single Cloranthy Ring can be found on each play through at the top of The Great Hollow. It is located inside the center trunk section. Jump across from one of the top branches to reach the ring.
It is possible to wear the Cloranthy Ring in-conjunction with other Stamina Regeneration items for an even quicker replenishment speed.