Horticulture/Verbascum thapsus

The Common Mullein or Great Mullein (Verbascum thapsus L.) is a species of mullein native to Europe and Asia. Other common names are Woolly Mullein, Flannel Mullein, Shepherd's Club, and Aaron's Rod. This dicotyledonous biennial is an introduced weed in several other parts of the world. It has been renowned since ancient times as a remedy for skin, throat and breathing ailment. The specific epithet thapsus is of unclear origins. It might be related to the African city of Thapsus, or the Greek establishment of Thapsos, now near Syracuse, Sicily.

Description


Common Mullein is a biennial that flowers for a month and a half in mid- to late summer. The first year it only produces a rosette of leaves. The second year it produces a tall stem that can reach up to 10 feet and ends in a dense spike of flowers, only a few of which flower at the same time. All parts of the plants are covered with star-shaped trichomes. The dried stem and fruits usually persist in winter.

The leaves are alternate, thick and decurrent, with a shape varying between oblong and oblanceolate and a size up to 4 inches across and 12 inches long (10.2 cm wide and 30.5 cm long). Their size diminishes as they get higher on the stem. The stem is solid (nearly an inch across) and is sometimes branched just below the inflorescence, typically doing so when damaged. The plants produces shallow taproots.



Flowers are pentamerous, with a 5-lobed calyx tube and corolla, the latter yellow and an inch or less wide, and five stamens. The flowers are almost sessile, with only very short pedicels (2 mm, 0.08 in). The three upper stamens are longer, with their filaments covered with yellow or whitish hair, while the two other stamen have glabrous filaments. The plant produces small (6 mm, 0.24 in) capsules containing large numbers of minute (less than a millimeter) brown seeds.

Ecology
The species is native to a wide range covering most of temperate Europe, parts of North Africa, Central Asia and the Himalayas. It was introduced and has naturalized in North America, Australia, Chile, Hispaniola and Argentina (1925). In the United States it was imported very early and cultivated for its medicinal property. By the 1630s, it was already escaped and had begun spreading so much that Amos Eaton thought it was a native plant, and gives it as such in 1818. In 1839 it is already reported in Michigan and in 1876, in California. It is now found commonly in all the states, and all the Canadian provinces.

Common Mullein is most frequent as a colonizer of disturbed soils. This is in part due to the plant's intolerance of shade and the very long periods that can extend before germination. It is not an agricultural weed, although its presence can be very difficult to completely eradicate, and is problematic in overgrazed pastures. It is considered a noxious weed in Colorado (Class C), Hawaii and Victoria, Australia (regionally prohibited in the West Gippsland region, and regionally controlled in several others).

This species favors dry, sandy or gravelly soils, although it can grow in a variety of habitats: meadows, roadsides, forest clearings and pastures. Common Mullein germinates almost solely in bare soil, in temperatures between 10 and 40°C (50F to 104F). While it can germinate in total darkness if proper conditions are present (tests give a 35% germination rate under ideal conditions), in nature, it will only appear if the seeds are exposed, or very close to the soil surface. While it can also appear in areas where some vegetation exist, growth of the rosettes on bare soil is four to seven times more rapid.

Common Mullein requires vernalization before it can flower. Plants that germinate in autumn overwinter if they are large enough (rosettes less than 15 cm (5,9 in) across die in winter) before flowering the next year. The entire plant usually dies at the end of its second year, although some rare individual remain vegetative a third year.

Individual flowers are open only for a day. They are autogamous and will self-fertilize if they haven't been pollinated by insects during the day. While many insects visit the flowers, only some bees will actually accomplish pollination. Visitors include Halictidae bees and hoverflies. Megachilidae bees, notably Anthidium species, use the hair in making their nests. Seeds are generally too small for birds to feed on, although the American Goldfinch was reported to consume them.

Common Mullein seeds maintain their germinative powers for decades, up to a hundred years, according to some studies. Because of this, and because the plant is an extremely prolific seed bearer (up to 180,000 or 240,000 ), it can sprout from apparently bare ground or shortly after forest fires long after previous plants have died, and will likely be an initial colonist. Common Mullein rarely establishes on new grounds without human intervention because its seeds are not dispersed very far. Seed dispersion requires the stem to be moved by wind or animal movement, and 75% of the seeds fall within a single meter of the parent plant; 93% fall within five meters.

Common Mullein is not considered an agricultural weed because it cannot compete with established plants, and is easily crowded out by them, except in areas where vegetation is sparse to begin with, such as Californian semi-desertic areas (Eastern Sierra Nevada), where it crowds out native herbs and grasses; Its tendency to appear after forest fires also disturbs the normal ecological succession. Despite not being an agricultural weed itself, it hosts a number of insects and diseases, including both pests and Beneficial insects. It is also a potential reservoir of the ../Cucumber Mosaic Virus. A study found V. thapsus to host insects from 29 different families. Most of the pests found were western flower thrips (../Frankliniella occidentalis/), ../Lygus/ species, such as the tarnished plant bug (../Lygus lineolaris/) and various ../Spider Mites/ from the family Tetranychidae. These make the plant a potential reservoir for overwintering pests. Other insects commonly found on Common Mullein are specific feeders such as mullein thrips (../Haplothrips/ verbasci), ../Gymnaetron tetrum/ and the Mullein Moth (../Cucullia verbasci/). Useful insects are also hosted by Common Mullein, including predatory mites of the ../Galendromus/, ../Typhlodromus/ and ../Amblyseius/ genera (Phytoseiidae), the minute pirate bug (../Orius tristicolor/) and the mullein plant bug (../Campylomma verbasci/).

Uses
Common Mullein has long had a medicinal reputation, especially as an astringent and emollient. It contains mucilage, several saponins, coumarin and rotenone. Dioscorides recommended it for diseases of the lung. Non medical uses have included dyeing and making torches.

Medical uses
2000 years ago, Dioscorides first recommended the plant 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 would be rapidly transmitted to the native Americans.

Oil from the flowers was used against catarrhs, colics and, in Germany, earaches, frostbite, eczema and other external problems. Topical application of various mullein-based preparation was recommended against warts, boils, carbuncles, and chilblains, amongst others. Recent studies have found Mullein (especially the flowers) to contain glycyrrhizin compounds with bactericide and potentially anti-tumoral action. In Germany, a governmental commission 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 as containing rotenone, although quantities are unknown.

In [Spanish, Common Mullein is called Gordolobo, a name transferred on Gnaphalium conoideum, a plant with a similar appearance and uses by the Mexican Aztecs, and the two are both sold under the name "Gordolobo," which has lead to at least one case of poisoning due to confusion with Senecio longilobus.

Other uses
Like many ancient plants (Pliny the Elder describes it in his Naturalis Historia), Common Mullein was linked to witches, although the relationship remained generally ambiguous, and the plant was also widely held as being able to ward off curses and evil spirits.

The flowers provide dyes of bright yellow or green, and have been used for hair coloring. The dried leaves and hair were made into candle wicks, or put into shoes to help with warmth keeping. The dried stems were also dipped into suet or wax to make torches.

Control


Control of the plant, when desired, is best managed via mechanical means, namely hand pulling and hoeing, preferably followed by sowing of native plants. Animals do not graze it because of its irritating hairs, and herbicides require surfactants to be effective, as the hair cause water to roll off the plant, much like the lotus effect. Burning is ineffective, as it only creates new bare areas for seedlings to colonize. G. tetrum and C. verbasci usually have little effect on V. thapsus populations. goats and chickens have been proposed to control Mullein. Effective (when used with a surfactant) contact herbicides include ../Glyphosate, triclopyr and ../Sulfurometuron-methyl/. Ground herbicides, like ../Tebuthiuron/, are also effective, but recreate bare ground and require repeated application to prevent regrowth.