The volcanic island is considered to be about three million years old (Pliocene); the other two islands in the archipelago, Mauritius and Rodrigues, are 7.8 million (Miocene) and 1​1⁄2 million (Pleistocene) years old, respectively. The island possesses a high endemism of flowering plants (about 225); this has justified the creation of a biological reserve on the lower slopes of the Piton des Neiges.