I think the most likely candidate is the Cuban treefrog, Osteopilus septentrionalis, but based on just that one picture, I can't say for sure. I will need to see more pictures from different angles. Chances are the plant came from Southern Florida, where this species has been introduced. If indeed it is a Cuban treefrog, be careful when handling it as this frog has toxic skin secretions. Wash your hands afterwards and never touch your face untill after you have done so. If you were to get these secretions in your eye you could be in a world of pain.