Aristolochia rotunda

The whole plant is poisonous. It contains aristolochic acids, which are known for their carcinogenic and mutagenic effects. In spite of this, it is the exclusive food for larvae of the beautiful and rare butterfly Zerynthia polyxena. Since larvae feed with the leaves, they themselves become poisonous. The poisons serve as a 'weapon' against their predators. Birds are very well informed about this fact! ( src)