麦角 is the fungus Claviceps purpurea, which infects rye and other grains and produces grain-shaped dark protrusions. Its alkaloids are the chemical ancestor of LSD (which was first synthesized from ergotamine by Albert Hofmann in 1938) and are still used medicinally for migraines and obstetric bleeding. Mass ergot poisoning in medieval Europe ("St. Anthony's Fire") caused gangrene and hallucinations.
