Notobubon galbanum, the notorious blister bush

The hairless, leathery leaves of Notobubon galbanum grow densely around the upper stems. These leaves are notorious for causing blisters, typically in a delayed action after a day or longer of having touched skin. The blisters are associated with photosensitivity induced by sunlight and the reaction is particularly severe when the plant has been bruised or when the touched skin is perspiring.

Like many plants with known toxicity, N. galbanum has nevertheless found its way into traditional medicine (Manning, 2007; Bean and Johns, 2005; Wikipedia).