Woolly Mullein (Verbascum thapsus)

Verbascum thapsus, the great mullein or common mullein, is a species of mullein native to Europe, northern Africa, and Asia, and introduced in the Americas and Australia.

It is a hairy biennial plant that can grow to 2 m tall or more. Its small, yellow flowers are densely grouped on a tall stem, which grows from a large rosette of leaves. It grows in a wide variety of habitats, but prefers well-lit, disturbed soils, where it can appear soon after the ground receives light, from long-lived seeds that persist in the soil seed bank.

It is a common weedy plant that spreads by prolifically producing seeds, and has become invasive in temperate world regions. It is a minor problem for most agricultural crops, since it is not a competitive species, being intolerant of shade from other plants and unable to survive tilling. It also hosts many insects, some of which can be harmful to other plants. Although individuals are easy to remove by hand, populations are difficult to eliminate permanently. Although commonly used in traditional medicine, there are no approved drugs from this plant, and it has been used to make dyes and torches.

V. thapsus is a dicotyledonous plant that produces a rosette of leaves in its first year of growth. The leaves are large, up to 50 cm long. The second-year plants normally produce a single unbranched stem, usually 1–2 m tall. The tall, pole-like stems end in a dense spike of flowers that can occupy up to half the stem length. All parts of the plants are covered with star-shaped trichomes. This cover is particularly thick on the leaves, giving them a silvery appearance.

On flowering plants, the leaves are alternately arranged up the stem. They are thick and decurrent, with much variation in leaf shape between the upper and lower leaves on the stem, ranging from oblong to oblanceolate, and reaching sizes up to 50 cm long and 14 cm across (19 inches long and 5 inches wide). They become smaller higher up the stem, and less strongly decurrent down the stem. The flowering stem is solid and 2–2.5 cm (nearly an inch) across, and occasionally branched just below the inflorescence, usually following damage. After flowering and seed release, the stem and fruits usually persist in winter, drying into dark brown, stiff structures of densely packed, ovoid-shaped, and dry seed capsules. The dried stems may persist into the following spring or even the next summer. The plant produces a shallow taproot.

Flowers are pentamerous with (usually) five stamen, a five-lobed calyx tube and a five-petalled corolla, the latter bright yellow and a 1.5–3 cm (0.59–1.18 in) wide. The flowers are almost sessile, with very short pedicels (2 mm, 0.08 in). The five stamens are of two types, with the three upper stamens being shorter, their filaments covered by yellow or whitish hairs, and having smaller anthers, while the lower two stamens have glabrous filaments and larger anthers.  The plant produces small, ovoid (6 mm, 0.24 in) capsules that split open by way of two valves, each capsule containing large numbers of minute, brown seeds less than 1 mm (0.04 in) in size, marked with longitudinal ridges. A white-flowered form, V. thapsus f. candicans, is known to occur. Flowering lasts up to three months from early to late summer,  with flowering starting at the bottom of the spike and progressing irregularly upward; each flower opens for part of a day and only a few open at the same time around the stem.

In the United States it was imported very early in the 18th century and cultivated for its medicinal and piscicide properties. By 1818, it had begun spreading so much that Amos Eaton thought it was a native plant.  In 1839 it was already reported in Michigan and in 1876, in California. It is now found commonly in all the states. 

Although long used in herbal medicine, no high-quality clinical research has been conducted on Verbascum thapsus as of 2018, and there are no drugs manufactured from its components. Dioscorides first recommended the plant 2000 years ago, believing it useful as a folk medicine for pulmonary diseases. Leaves were smoked to attempt to treat lung ailments, a tradition that in America was rapidly transmitted to Native American peoples. The Zuni people, however, use the plant in poultices of powdered root applied to sores, rashes and skin infections. An infusion of the root is also used to treat athlete's foot. All preparations meant to be drunk have to be finely filtered to eliminate the irritating hairs.

Roman soldiers are said to have dipped the plant stalks in grease for use as torches. Other cultures use the leaves as wicks. Native Americans and American colonists lined their shoes with leaves from the plant to keep out the cold.