Image Credit: James H. Miller & Ted Bodner, Southern Weed Science Society, Bugwood.org - See more at: http://www.invasive.org/browse/detail.cfm?imgnum=1120270#sthash.uP13TQ7E.dpuf
Center for Aquatic and Invasive Plants
Description: This is a biennial herb with felt-like leaves. It was originally introduced to Virginia as a piscicide in the mid-1700s. Furthermore it spread rapidly due to its medicinal uses. In the first year this plant has low growing rosettes while in the second year it is a 5-10 feet tall flowering stalk. These flowers are bright yellow with five petals and bloom from June- August. Flowers are about one inch wide and only a few bloom at a time. Common mullein leaves are alternately arranged down the stalk with the largest leaves at the base. The leaves are bluish-green and can be 12 inches long by 5 inches wide. This plant has small pitted seeds that have the capability of lying dormant for decades.
Ecological Threat: Natural meadows and forest openings are threatened by this invasive plant. Because common mullein is extremely adaptable it can invade these places and displace native plants. This plant produces large numbers of seeds that can lay dormant for years before germinating. This is a pioneer plant, so it is one of the first things to grow in a disturbed area.
Biology & Spread: This invasive is on a two year cycle of growth, flowering, and death (monocarpic perennial). The first year of the cycle produces a taproot and large rosette of leaves. In the second year of the cycle the plant rapidly grows a tall stalk. This stalk produces flowers from the tip of the stalk to the base of the plant. After the summer of the second year of growth the plant produces seeds. One individual can produce 100,000 to 180,000 seeds. These seeds are released in close proximity to the plant and can remain viable for over 100 years. The invasive common mullein prefers dry and sandy soils, but is adaptable to many soil types. It is especially adaptable to disturbed sites where dormant seeds can germinate. This plant does well in areas with a mean annual precipitation of 3-6 inches and is not shade tolerant.
Threat in Oklahoma: This plant grows faster than many native species, giving it a competitive advantage. The dormant seeds easily grow in disturbed areas.