sulfur dioxide: a colorless toxic gas (SO2) that occurs in the gases from volcanoes; used in many manufacturing processes and present in industrial emissions; causes acid rain
pollutant: waste matter that contaminates the water or air or soil
lesser celandine: perennial herb native to Europe but naturalized elsewhere having heart-shaped leaves and yellow flowers resembling buttercups; its tuberous roots have been used as a poultice to relieve piles