Digitalis purpurea, popularly called foxglove or digital, among many other names

The distinctive flower of the foxglove—whose thimble-like shape gave it its name—and its leaves contain a powerful toxin, digitalin, which affects heart function. Extremely poisonous if consumed, the extract of the active ingredient has been used as a medication for arrhythmia and other cardiac deficiencies since the late 18th century.