Oenanthe crocata, the hemlock water-dropwort, is a flowering plant in the carrot family, Apiaceae. Scientists at the University of Eastern Piedmont in Italy wrote that they had identified Oenanthe crocata as the plant responsible for producing the sardonic grin.This plant is a possible candidate for the "sardonic herb", which was a neurotoxic plant referred to in ancient histories.
Deadhead regularly to prevent unwanted seedlings. Cut back in autumn. Wear protective gloves and coveralls and carefully dispose of cut material.