Mullein is a member of the figwort family with hairy leaves and tall, yellow spikes of flowers. It originates in Europe, where it has been used since ancient times. Mullein leaves contain large amounts of a soluble fiber known as mucilage, a thick, gelatinous substance. It is believed that the mucilage contributes to mullein's soothing effects. Mullein leaves may provide nutritive support for healthy respiratory and bronchial function.