A biennial plant with grayish white, woolly leaves, the common mullein (Verbascum thapsus) is also called flannel plant or Aaron's rod because it is tall and spear-like in habit. In Carravaggio's painting "Saint John the Baptist," made in the early 17th century, the plant at the feet of St. John is the common mullein. It produces lots of seeds that are also eaten by birds, spread around the landscape in their droppings. This biennial grows widespread across USDA Hardiness Zones 3 through 9.
Native to sunny meadows and woodland clearings, common mullein's natural range is from Europe into extreme western Asia. According to Missouri Plants Online, it was among the first plants brought to North America by Europeans. The Plant Conservation Alliance records that it was introduced into Virginia in the 1700s, where it was used as a fish poison. Since then, this plant has naturalized across the continent in habitats like roadsides, pastures, unmanaged fields, waste ground, disturbed sites and railroad alleys.
In the first year of growth, common mullein is a tufted basal rosette of whitish gray, fuzzy leaves that is about 12-inches tall and 12- to 24-inches wide. It overwinters and then in the second growing season it send up a narrow, sturdy stem 4- to 6-feet tall, sparsely lined in leaves. At the top of the stem is a clustered line of numerous tiny yellow flowers that are saucer-shaped, lasting from late spring to midsummer. Butterflies and bees pollinate them, resulting in the production of as many as 100,000 to 180,000 seeds on a single plant, according to the Plant Conservation Alliance. The fall frost kills the plant in the second year, but the tall stem persists like a skeleton into the third year before toppling.
Common mullein prospers in abundant sunshine locations where the soil is neutral to alkaline in pH. It is one of the few plants that establishes readily in nutrient-poor or seemingly drier soils. The Plant Conservation Alliance notes this plant grows in regions where as little as 3 to 6 inches of rainfall occurs annually. If growing on fertile ground, the plants are lusher and faster growing but tend to be less rigid and will bend and flop over in wind and rain. It readily reseeds itself in the landscape as it snaps open its seed capsules to thrust seeds far from the mother plant. Seeds germinate better in loose, crumbly soils.
The Plant Conservation Alliance regards common mullein as a noxious weed since it populates poor soil sites where native grasses and wildflowers also naturally grow. The mullein's copious production of seeds readily out-competes native plants. Fortunately, mullein plants are easily pulled up, as their taproots are not too deep.
Common mullein leaves contain coumarins and other trace toxins. Traditionally, medicinal uses included as a remedy for coughs and diarrhea and a respiratory stimulant for the lungs when smoked. A methanol extract from common mullein has been used as an insecticide for mosquito larvae.