| Verbascum thapsus | |
|---|---|
 | |
| Second-year plant starting to flower, with a dead stem of the previous year, behind left | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Asterids |
| Order: | Lamiales |
| Family: | Scrophulariaceae |
| Genus: | Verbascum |
| Species: | V. thapsus |
| Binomial name | |
| Verbascum thapsus | |
Verbascum thapsus, thegreat mullein,greater mullein orcommon mullein, is a species ofmullein native to Europe, northern Africa, and Asia, and introduced in the Americas, Australia and New Zealand.[1]
It is a hairybiennial 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 largerosette 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 thesoil seed bank. It is a commonweedy plant that spreads by prolifically producing seeds, and has becomeinvasive in temperate world regions.[1] 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 survivetilling. 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 intraditional medicine, noapproved drugs are made from this plant.[2] It has been used to makedyes andtorches.[1]
V. thapsus is adicotyledonous plant that produces arosette of leaves in its first year of growth.[3][4] 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 eastern part of its range in China, it is, however, only reported to grow up to 1.5 m tall.[5] The tall, pole-like stems end in a densespike of flowers[3] that can occupy up to half the stem length. All parts of the plants are covered with star-shapedtrichomes.[5][6] This cover is particularly thick on the leaves, giving them a silvery appearance. The species'chromosome number is 2n = 36.[7]
On flowering plants, the leaves are alternately arranged up the stem. They are thick anddecurrent, with much variation in leaf shape between the upper and lower leaves on the stem, ranging fromoblong to oblanceolate, and reaching sizes up to 50 cm long and 14 cm across (19 inches long and 5 inches wide).[8][9] They become smaller higher up the stem,[3][4] and less strongly decurrent down the stem.[3] The flowering stem is solid and 2–2.5 cm (nearly an inch) across, and occasionally branched just below theinflorescence,[4] usually following damage.[10] After flowering and seed release, the stem and fruits usually persist in winter,[11] 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 shallowtaproot.[9]
Flowers are pentamerous with (usually) fivestamen, a five-lobedcalyx tube, and a five-petalledcorolla, the latter bright yellow and an 1.5–3 cm (0.59–1.18 in) wide. The flowers are almostsessile, with very shortpedicels (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 smalleranthers, while the lower two stamens haveglabrous filaments and larger anthers.[6][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, brownseeds less than 1 mm (0.04 in)[12] in size, marked with longitudinal ridges. A white-flowered form,V. thapsus f.candicans, is known to occur.[13] Flowering lasts up to three months from early to late summer (June to August in northern Europe),[4] 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.[11]
For the purpose ofbotanical nomenclature,Verbascum thapsus was first described byCarl Linnaeus in his 1753Species Plantarum. Thespecific epithetthapsus had been first used byTheophrastus (asΘάψος,Thapsos)[14] for an unspecified herb from theAncient Greek settlement ofThapsos, near modernSyracuse,Sicily,[14][15] though it is often assimilated to the ancientTunisian city ofThapsus.[16]
At the time, notype specimen was specified, as the practice only arose later, in the 19th century. When a lectotype (type selected amongst original material) was designated, it was assigned to specimen 242.1 of Linnaeus' herbarium, the onlyV. thapsus specimen.[note 2] The species had previously been designated astype species forVerbascum.[18] European plants exhibit considerablephenotypical variation,[19] which has led to the plant acquiring manysynonyms over the years.[17][20] Introduced American populations show much less variation.[19]
The taxonomy ofVerbascum has not undergone any significant revision since Svanve Mürbeck's monographs in the 1930s, with the exception of the work of Arthur Huber-Morath, who used informal grouping in organizing the genus for the florae of Iran and Turkey to account for many intermediate species. Since Huber-Morath's groups are not taxonomical, Mürbeck's treatment is the most current one available, as no study has yet sought to apply genetic or molecular data extensively to the genus. In Mürbeck's classification,V. thapsus is placed in sect.Bothrospermae subsect.Fasciculata alongside species such asVerbascum nigrum (black or dark mullein),Verbascum lychnitis (white mullein), andVerbascum sinuatum (wavy-leaved mullein).[21][22][23][24] AsVerbascum thapsus is the type species of the genus the application of article 22 of theICNafp gives sect.Verbascum subsect.Verbascum as the correct nomenclature for this placement.
| Hybrid name | Other parent species | Notes |
|---|---|---|
| V. × duernsteinense Teyber | V. speciosum | |
| V. × godronii Boreau | V. pulverulentum | |
| V. × kerneri Fritsch | V. phlomoides | |
| V. × lemaitrei Boreau | V. virgatum | |
| V. × pterocaulon Franch. | V. blattaria | |
| V. × thapsi L. | V. lychnitis | syn.V. × spurium W.D.J.Koch, may be a nomen ambiguum[26] |
| V. × semialbum Chaub. | V. nigrum | |
| none | V. pyramidatum |
The three usually recognizedsubspecies are:
In all subspecies but the type, the lower stamens are also hairy.[28] InV. t. crassifolium, the hairiness is less dense and often absent from the upper part of the anthers, while lower leaves are hardly decurrent and have longer petioles.[27] InV. t. giganteum, the hairs are densely white tomentose, and lower leaves are strongly decurrent.V. t. crassifolium also differs from the type in having slightly larger flowers, which measure 15–30 mm wide, whereas in the type, they are 12–20 mm in diameter.[27] BothV. t. giganteum andV. t. crassifolium were originally described as species.[3] Due to its morphological variation,V. thapsus has had a great many subspecies described. A recent revision led its author to maintainV. giganteum but sinkV. crassifolium into synonymy.[24]
The plant is also parent to several hybrids (see table). Of these, the most common isV. × semialbum Chaub. (×V. nigrum).[7] All occur in Eurasia,[7] and three,V. × kerneri Fritsch,V. × pterocaulon Franch. andV. × thapsi L. (syn.V. × spurium W.D.J.Koch), have also been reported in North America.[25][29]
V. thapsus is known by a variety of names. European reference books call it "great mullein".[30][31][32] In North America, "common mullein" is used[33][34] while western United States residents sometimes refer to mullein as "cowboy toilet paper".[35][36]
In the 19th century, it had well over 40 different common names in English alone. Some of the more whimsical ones included "hig candlewick", "Indian rag weed", "bullicks lungwort", "Adams-rod", "hare's-beard", and "ice-leaf".[37] Vernacular names include innumerable references to the plant's hairiness: "woolly mullein", "velvet mullein", or "blanket mullein",[32][38] "beggar's blanket", "Moses' blanket", "poor man's blanket", "Our Lady's blanket", or "old man's blanket",[31][34][39] and "feltwort", and so on ("flannel" is another common generic name). "Mullein" itself derives from the French word for "soft".[40]
Some names refer to the plant's size and shape: "shepherd's club(s)" or "staff", "Aaron's rod"[41] (a name it shares with a number of other plants with tall, yellow inflorescences), and a plethora of other "X's staff" and "X's rod".[31][34][42] The name "velvet dock" or "mullein dock" is also recorded, where "dock" is a British name applied to any broad-leaved plant.[43]
V. thapsus has a wide native range including Europe, northern Africa, and Asia, from theAzores andCanary Islands east to westernChina, north to theBritish Isles,Scandinavia, andSiberia,Kashmir[44] and south to theHimalayas.[5][45][46] In northern Europe, it grows from sea level up to 1,850 m altitude,[4] while in China it grows at 1,400–3,200 m altitude.[5]
It has been introduced throughout the temperate world, and isestablished as aweed inAustralia,New Zealand, tropical Asia,La Réunion, North America,Hawaii,Chile,Hispaniola, andArgentina.[46][47][48][49] It has also been reported inJapan.[50]
In the United States, it was imported very early in the 18th[note 3] century and cultivated for its medicinal andpiscicide properties. By 1818, it had begun spreading so much thatAmos Eaton thought it was a native plant.[note 4][9][51] In 1839, it was already reported inMichigan and in 1876, inCalifornia.[9] It is now found commonly in all the states.[52] InCanada, it is most common in theMaritime Provinces and southernQuebec,Ontario, andBritish Columbia, with scattered populations in between.[19][53]
Great mullein most frequently grows as a colonist of bare and disturbed soil, usually on sandy or chalky ones.[7] 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 strongphenotype variation rather thanadaptation capacities.[54]
Great mullein is a biennial and generally requireswinter dormancy before it can flower.[10] This dormancy is linked tostarch degradation activated by low temperatures in the root, andgibberellin application bypasses this requirement.[55] Seeds germinate almost solely in bare soil, at temperatures between 10 and 40 °C.[10] While they can germinate in total darkness if proper conditions are present (tests give a 35% germination rate under ideal conditions), in the wild, they in practice only do so when exposed to light, or very close to the soil surface, which explains the plant's habitat preferences. While it can also grow in areas where some vegetation already exists, growth of the rosettes on bare soil is four to seven times more rapid.[10]
Seeds germinate in spring and summer. Those that germinate in autumn produce plants that overwinter if they are large enough, while rosettes less than 15 cm (6 in) across die in winter. After flowering, the entire plant usually dies at the end of its second year,[10] but some individuals, especially in the northern parts of the range, require a longer growth period and flower in their third year. Under better growing conditions, some individuals flower in the first year.[56] Triennial individuals have been found to produce fewer seeds than biennial and annual ones. While year of flowering and size are linked to the environment, most other characteristics appear to be genetic.[57]
A given flower is open only for a single day, opening before dawn and closing in the afternoon.[19] Flowers areself-fecundating andprotogynous (with female parts maturing first),[19] and will self-pollinate if they have not beenpollinated by insects during the day. While many insects visit the flowers, only some bees actually accomplish pollination. The flowering period ofV. thapsus lasts from June to August in most of its range, extending to September or October in warmer climates.[9][10][12] Visitors includehalictid bees andhoverflies.[11] The hair on lower stamens may serve to provide footholds for visitors.[19]
The seeds maintain their germinative powers for decades, up to 100 years, according to some studies.[58] Because of this, and because the plant is an extremely prolific seed bearer (each plant produces hundreds of capsules, each containing up to 700 seeds,[19] with a total up to 180,000[9][10] or 240,000[12] seeds), it remains in thesoil seed bank for extended periods of time, and can sprout from apparently bare ground,[10] or shortly afterforest fires long after previous plants have died.[12] Its population pattern typically consists of an ephemeral adult population followed by a long period of dormancy as seeds.[19] Great mullein rarely establishes on new grounds without human intervention because its seeds do not disperse very far.Seed dispersion requires the stem to be moved by wind or animal movement; 75% of the seeds fall within 1 m of the parent plant, and 93% fall within 5 m.[10]
Megachilid bees of the genusAnthidium use the hair (amongst that of various woolly plants) in making theirnests.[59] The seeds are generally too small for birds to feed on,[11] although theAmerican goldfinch has been reported to consume them.[60] Other bird species have been reported to consume the leaves (Hawaiian goose)[61] or flowers (palila),[62] or to use the plant as a source whenforaging for insects (white-headed woodpecker).[63] Additionally, deer and elk eat the leaves.[64]
Seeds ofV. thapsus have been recorded from part of theCromer Forest Bed series and atWest Wittering inSussex from some parts of theIpswichian interglacial layers.[65]
Because it cannot compete with established plants, great mullein is no longer considered a serious agricultural weed and is easily crowded out in cultivation,[19] except in areas where vegetation is sparse to begin with, such asCalifornian semidesertic areas of the easternSierra Nevada in the USA. In such ecological contexts, it crowds out native herbs and grasses; its tendency to appear after forest fires also disturbs the normalecological succession.[10][12] Although not an agricultural threat, its presence can be very difficult to eradicate and is especially problematic inovergrazed pastures.[9][10][12] The species is legally listed as anoxious weed in the US state ofColorado (class C)[66] and Hawaii,[67] and the Australian state ofVictoria (regionally prohibited in theWest Gippsland region, and regionally controlled in several others).[68]
Despite not being an agricultural weed in itself, ithosts a number of insects anddiseases, including bothpests andbeneficial insects.[69] It is also a potential reservoir of thecucumber mosaic virus,Erysiphum cichoraceum (the cucurbitpowdery mildew) andTexas root rot.[19][70] A study foundV. thapsus hosts insects from 29 differentfamilies. Most of the pests found werewestern flower thrips (Frankliniella occidentalis),Lygus species such as thetarnished plant bug (L. lineolaris), and various spider mites from the familyTetranychidae. These make the plant a potential reservoir foroverwintering pests.[69]
Other insects commonly found on great mullein feed exclusively onVerbascum species in general orV. thapsus in particular. They include mullein thrips (Haplothrips verbasci),[69]Gymnaetron tetrum (whose larva consume the seeds), and themullein moth (Cucullia verbasci).[9] Useful insects are also hosted by great mullein, including predatory mites of the generaGalendromus,Typhlodromus, andAmblyseius, theminute pirate bugOrius tristicolor,[69] and themullein plant bug (Campylomma verbasci).[71] The plant's ability to host both pests and beneficials makes it potentially useful to maintain stable populations of insects used for biological control in other cultures, likeCampylomma verbasci andDicyphus hesperus (Miridae), a predator ofwhiteflies.[72][73] A number of pestLepidoptera species, including thestalk borer (Papaipema nebris) andgray hairstreak (Strymon melinus), also useV. thapsus as a host plant.[74]
Control of the plant, when desired, is best managed via mechanical means, such as hand pulling and hoeing, preferably followed by sowing of native plants. Animals rarelygraze it because of its irritating hairs, and liquidherbicides requiresurfactants to be effective, as the hair causes water to roll off the plant, much like thelotus effect. Burning is ultimately ineffective, as it only creates new bare areas forseedlings to occupy.[9][10][12]G. tetrum andCucullia verbasci usually have little effect onV. thapsus populations as a whole.[12] Goats and chickens have also been proposed to control mullein.[10] Effective (when used with a surfactant) contact herbicides includeglyphosate,[9][12]triclopyr[9] andsulfurometuron-methyl.[12] Ground herbicides, liketebuthiuron, are also effective, but they result in bare ground – ideal conditions for growing more mullein – and therefore require repeated application to prevent regrowth.[10]
Phytochemicals inV. thapsus flowers and leaves includesaponins,polysaccharides,mucilage,flavonoids,tannins,iridoid andligninglycosides, andessential oils.[2] The plant's leaves, in addition to the seeds, have been reported to containrotenone, although quantities are unknown.[75]
Although long used inherbal medicine, nodrugs are manufactured from its components.[2]Dioscorides first recommended the plant 2000 years ago, considering it useful as afolk medicine for pulmonary diseases.[76] Leaves were smoked to attempt to treat lung ailments, a tradition that in America was rapidly transmitted toNative American peoples.[31][77] TheZuni people, however, use the plant inpoultices of powdered root applied tosores,rashes, and skin infections. An infusion of the root is also used to treatathlete's foot.[78] All preparations meant to be drunk have to be finely filtered to eliminate the irritating hairs.[55]
Oil from the flowers was used againstcatarrhs,colics,earaches,frostbite,eczema, and other external conditions.[31] Topical application of variousV. thapsus-based preparations was recommended for the treatment ofwarts,[79]boils,carbuncles, hemorrhoids, andchilblains, amongst others.[31][77]Glycyrrhizin compounds withbactericide effects in vitro were isolated from flowers.[80] The GermanCommission E describes uses of the plant for respiratory infections.[81] It was also part of theNational Formulary in the United States[77] and United Kingdom.[31]
The plant has been used in an attempt to treat colds,croup, sunburn, and other skin irritations.[82]
Roman soldiers are said to have dipped the plant stalks in grease for use as torches. Other cultures use the leaves as wicks.[82] Native Americans and American colonists lined their shoes with leaves from the plant to keep out the cold.[82][31][77]
Mullein may be cultivated as anornamental plant.[1] As with many plants, (Pliny the Elder described it in hisNaturalis Historia),[note 5] great mullein was linked towitches,[31] although the relationship remained generally ambiguous, and the plant was also widely held to ward offcurses andevil spirits.[31][55][76][77] The seeds contain several compounds (saponins,glycosides,coumarin,rotenone) that are toxic to fish, and have been widely used aspiscicide forfishing.[9][84]
Due to its weedy capacities, the plant, unlike other species of the genus (such asV. phoeniceum), is not often cultivated.[1]
