At the beginning of each end step, each player who tapped a land for mana this turn sacrifices a land of their choice. This enchantment deals 2 damage to each player who sacrificed a Plains this way.
It works even if it was not on the battlefield when the land was tapped for mana.
Each Desolation only causes up to one land per turn to be sacrificed. If you have more than one, each will do this.