When yellow flag iris (Iris pseudacorus) is in bloom, in late spring/early summer, it’s as striking as other varieties in the iris family. But this plant, native to Europe, Great Britain, North America and the Mediterranean, but its beauty masks the danger to humans and livestock. It will make livestock sick if they eat it and contact with the resin will cause skin irritation to humans. If you are trying to remove yellow flag iris, be sure to wear gloves and long-sleeves. It usually grows along waterways and in wetlands and spreads quickly by rhizome.