Verbascum 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. In the East of its range in China, it is, however, only reported to grow up to 1.5 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. The species' chromosome number is 2n = 36. 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. A closeup of the flowersFlowers are pentamerous with (usually) five stamen, a 5-lobed calyx tube and a 5-petalled corolla, the latter bright yellow and an 1.5–3 cm (0.5–1 inch) 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.[note 1] 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 a millimetre (0.04 in) in size, marked with longitudinal ridges. A white-flowered form, V. thapsus f. candicans, is known to occur. Flowering lasts for up to three months from early to late summer (June to August in northern Europe), 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.[
Verbascum thapsus has a wide native range including Europe, northern Africa and Asia, from the Azores and Canary Islands east to western China, north to the British Isles, Scandinavia and Siberia, and south to the Himalayas. In northern Europe, it grows from sea level up to 1,850 m altitude, while in China it grows at 1,400–3,200 m altitude. It has been introduced throughout the temperate world, and is established as a weed in Australia, New Zealand, tropical Asia, La Réunion, North America, Hawaii, Chile, Hispaniola and Argentina. It has also been reported in Japan. In the United States it was imported very early in the 18th[note 3] century and cultivated for its medicinal and piscicide property. By 1818, it had begun spreading so much that Amos Eaton thought it was a native plant.[note 4] In 1839 it was already reported in Michigan and in 1876, in California. It is now found commonly in all the states. In Canada, it is most common in the Maritime Provinces as well as southern Quebec, Ontario and British Columbia, with scattered populations in between. Great Mullein most frequently grows as a colonist of bare and disturbed soil, usually on sandy or chalky ones. It grows best in dry, sandy or gravelly soils, although it can grow in a variety of habitats, including banksides, meadows, roadsides, forest clearings and pastures. This ability to grow in a wide range of habitats has been linked to strong phenotype variation rather than adaptation capacities.
Great Mullein has been used since ancient times as a remedy for skin, throat and breathing ailments. It has long had a medicinal reputation, especially as an astringent and emollient, as it contains mucilage, several saponins, coumarin and glycosides. Dioscorides recommended it for diseases of the lung and it is now widely available in health and herbal stores. Non-medical uses have included dyeing and making torches.  Medical usesDioscorides first recommended the plant 2000 years ago, against pulmonary diseases, and this has remained one of its primary uses, especially against cough. Leaf decoctions or herbal teas were used for expectoration, consumption, dry cough, bronchitis, sore throat and hemorrhoids. Leaves were also smoked against pulmonary ailments, a tradition that in America was rapidly transmitted to Native American peoples. They used the non-indigenous plant to make syrups against croup. The combination of expectorant saponins and emollient mucilage makes the plant particularly effective for cough. All preparations meant to be drunk have to be finely filtered to eliminate the irritating hairs. Oil from the flowers was used against catarrhs, colics and, in Germany, earaches, frostbite, eczema and other external conditions. Topical application of various V. thapsus-based preparations was recommended for the treatment of warts, boils, carbuncles, hemorrhoids, and chilblains, amongst others. Recent studies have found that Great Mullein contains glycyrrhizin compounds with bactericide and potential anti-tumoral action. These compounds are concentrated in the flowers. Different extracts have varying levels of efficiency against bacteria. The German Commission E sanctioned medicinal use of the plant for catarrhs. It was also part of the National Formulary in the United States and United Kingdom. The plant's leaves, in addition to the seeds, have been reported to contain rotenone, although quantities are unknown.[