This description provides characteristics that may be relevant to fire ecology and is not meant for identification. Keys for identification are available (e.g., [41,45,47,58,143,144,147]).
Aboveground characteristics: Common mullein is a densely woolly, sturdy biennial that may reach more than 7 feet (2 m) tall in its flowering year [36,66,113,144]. Annual and triennial forms occasionally occur [110]. A basal rosette of large furry leaves and a substantial crown are produced in the first year [10]. In the second year, common mullein typically produces a single, stout (>1 cm thick), erect flowering stem. One or more erect branches near the base of the inflorescence are normal [56,104,131]. Basal leaves are simple, measure 3 to 20 inches (8-50 cm) long, and may be persistent. Stem leaves are alternate, and their size is reduced toward the inflorescence [30,104,144]. The thick coating of branched hairs on the stems and leaves breaks the force of surface winds and prevents water loss to evaporation [10].
Common mullein flowers are densely arranged on a spike-like, terminal inflorescence [59,78,106]. Flowers are short-lived. They are open to pollination for 1 day from just before dawn to midafternoon (Thompson, personal communication, cited in [52]). Branching of the inflorescence can occur with herbivory or clipping damage [87,89], and duration of flowering is a function of flowering stalk length. Long stalks may flower late into the growing season [52]. Fasciation or unregulated tissue growth that forms a large, bulbous inflorescence occurs often in Hawaiian common mullein populations. The frequency of fasciated flowers ranges from 0% to 45%, and fasciated plants have occurred on the Island for 50 years or more [7,33]. This phenomenon is discussed more in Seed production and Impacts and Control.Fasciated inflorescence
© Gerald D. Carr
Common mullein produces hairy, egg-shaped, two-celled capsules. Capsules are 6 to 10 mm long, split at maturity, and contain numerous seeds. Seeds are small, 0.4 to 0.8 mm long, and average 0.064 mg. Seeds are wingless and not adapted for long-distance dispersal [52,53,56,58,97,104,144]. The rod-like spike of fruits often persists through the winter [143].
Belowground characteristics: Thick, deep taproots with fibrous lateral roots are produced in the first year of rosette growth. Root growth nearly stops when common mullein bolts (Reinartz, unpublished data, cited in [111]), [10,104,144]. As of this writing (2008), no excavation studies reported taproot size or rooting depth. A study by Reinartz [111], however, suggests that root size and rooting depth may vary by site. When common mullein plants from seed collected at increasing latitudes were grown in a common garden, plants from southern seed sources (Texas or Georgia) had a significantly (P<0.01) greater proportion of root biomass than plants from seed collected in North Carolina or southern Canada.
Common mullein is a nonnative species that occurs throughout most of North America. In Canada, common mullein is found in all southern provinces. In the United States, common mullein occurs in all states including Alaska and Hawaii [7,104,113,139]. Within the contiguous United States, common mullein is often described as common, widespread, conspicuous, or everywhere [36,41,47,66,92,106,130,143,147]. Plants Database provides a map of common mullein's North American distribution.
In much of the United States, common mullein is considered adventive or naturalized [47,96,97,144]. Common mullein was likely introduced to the eastern United States more than 230 years ago. Before the Revolutionary War, common mullein seeds were brought and cultivated by early settlers for the easy collection of fish [148]. It is likely other initial introductions occurred as well, and given the many uses of common mullein, it was likely transported and cultivated by US settlers and tribes. For more on the use of common mullein by early European settlers and Native Americans, see Other Uses.
While the method and speed of common mullein's spread across the United States is not well known, it was noted as a common weed in Boulder County, Colorado, in 1905 [154] and was observed in Mount Rainier National Park, Washington, in 1932 [124]. Introduction(s) into Alaska may have been more recent, as common mullein was not recorded in the state's flora published in 1968 [61]. Common mullein was first reported in Hawaii in 1932, and as of 1990, it occupied an area greater than 770 mile² (2,000 km²) [31].
In most places, common mullein is limited to disturbed areas and rarely persists beyond the earliest stages of succession. A 2004 report from the Forest Service's Eastern Region lists common mullein as a widespread nonnative species typically restricted to disturbed areas and not particularly invasive in undisturbed habitats [138]. However, persistent and unusually dense populations are reported in some Hawaii [33] and California [16] habitats. Potential effects of common mullein's persistence in these areas are addressed in Impacts and Control.
Fire adaptations: Common mullein is typical in early postfire communities [14,23,24,86]. In most cases, common mullein establishes from soil-stored seed on burned sites. For additional information, see Plant Response to Fire.
FIRE REGIMES: The prevailing fire regime in which common mullein evolved is not described in the available literature. FIRE REGIMES in North American common mullein habitats are difficult to characterize, since common mullein occurs in nearly any vegetation type. Because common mullein is a rapidly reproducing, early-seral species, it is unlikely that frequent fire would eliminate it. The persistent common mullein seed bank suggests that long fire-return intervals would likely be tolerated too.
Common mullein fuel characteristics were not described in the reviewed literature, and dense common mullein populations are normally short-lived. Persistent dense populations are described in California meadows and in subalpine and alpine regions of Hawaii. As of this writing (2008), effects of these persistent common mullein stands on fire frequency or fire severity were not described. Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find FIRE REGIMES".
Common mullein occupies open sites. It is often described on disturbed sites such as roadsides, shores, fields, clearings, and vacant lots throughout its range [30,78,104,143,147] but is possible in any habitat without dense cover [41].
Climate: Common mullein tolerates a wide variety of growing conditions. Wide ecological amplitude has likely been more important than adaptation to local conditions in establishment and spread of this species. When common mullein seed collected from different elevations (246-7,421 feet (75-2,262 m)) in California [102] and in Hawaii [7] was grown in a common garden, relationships between elevation and distinctive plant traits were rare. Researchers in California suggested that common mullein has a "general-purpose genotype" [102]. Results were similar when seedlings from seed collected in Texas, Colorado, and Alberta were grown in a common area. Seedlings had similar photosynthetic rates at temperatures from 68 to 95 °F (20-35 °C). Although photosynthetic rates were higher at the coldest temperatures for plants from seed collected in cool habitats, researchers indicated that wide-ranging tolerances and not rapid local adaptation was most important to common mullein's wide distribution and success [149].
Differences in climate, latitude, and associated vegetation may affect development and life history of common mullein populations from southern Canada, North Carolina, Texas, and Georgia. In southern Canada, the growing season is short and precipitation ample and reliable. In North Carolina and Georgia, precipitation is abundant, and the growing season is long. In Texas, the growing season can be cut short by drought conditions. Sites in southern Canada with sparse vegetation had the most common mullein plants that did not flower until 3 or 4 years old. Annual common mullein plants were most common in Georgia, where associated vegetation cover increased to nearly 100% in 2 growing seasons. The most rapid annual development occurred in populations from southwestern Texas, where annual precipitation was lowest and hard frosts were uncommon [109,110]. The largest common mullein plants occurred on Texas sites with favorable moisture [111].
Life history differences between common mullein populations from southern Canada to Texas and Georgia [110] Population location, number Probability of fruitingProportion fruiting as
annuals biennials triennials Southern Canada, n=10 0.52 0 0.92 0.13 North Carolina, n=6 0.64 0 0.93 0.05 Texas, n=6; Georgia, n=2 0.62 0.27 0.73 0.01Elevation: In Hawaii, common mullein occupies sites from near sea level to 4,596 m (15,080 feet) [7]. Elevation tolerances are not as wide for the rest of the United States.
Elevation range for common mullein in the western United States State Elevation (feet) Arizona 5,000-7,000 [67]Soils: Soil type is probably not important in limiting common mullein establishment or successful reproduction. Common mullein is described on "light" soils in Nova Scotia [113], "heavy" soils in Wisconsin [32], coarse soils in the Great Plains [131], and well-drained soils in the Adirondack Uplands [75]. Reinartz, who studied common mullein populations from southern Canada to Georgia and Texas, indicated that common mullein "thrives" on dry, infertile, highly calcareous soils as long as sunlight is abundant [109].
Impacts: In many areas and vegetation types, common mullein is a short-lived member of disturbed communities whose abundance decreases with increased time since disturbance. In 1999 the California Invasive Plant Council listed common mullein as a "wildland pest plant of lesser invasiveness" because its spread and degree of habitat disruption were less than the area's other pest plants [20]. As of 2004, a Forest Service report lists common mullein as a widespread nonnative species that is generally restricted to disturbed sites and not especially invasive in undisturbed habitats in the eastern United States [138]. However, in parts of California and in Hawaii, common mullein may form dense and persistent populations [7,16,31,144].
In moist meadows and drainages of California's Mono Lake and Owens Valley, common mullein populations can be abundant. Common mullein has also colonized intact and undisturbed meadows in this area. In the western Sierra Nevada, common mullein establishes almost immediately following fire. Although common mullein is eventually replaced by regenerating shrubs, it may restrict the establishment of native early-seral forbs and grasses and disrupt normal succession in the Sierra Nevada [16].
High density common mullein populations are common in Hawaii. Common mullein has colonized habitats from near sea level to near the Mauna Kea summit at 15,080 feet (4,600 m) [7,33]. As of a 1990 review, common mullein occupied over 2,000 km² area. Densities as high as 190 plants/100 m² have been reported on disturbed areas of Mauna Kea, although common mullein is also widely established and often abundant and persistent in relatively undisturbed subalpine grasslands dominated by alpine hairgrass (Deschampsia nubigena), subalpine woodlands dominated by ohia lehua (Metrosideros polymorpha), and in alpine desert communities [7,31,144]. Common mullein plants in Hawaii frequently form an odd-shaped, fasciated inflorescence capable of seed production 3 times that of normal flowers (Daehler, unpublished data, cited in [33]).
Common mullein is also considered disruptive to the recruitment of native flora in Hawaii [33]. In subalpine vegetation on Mauna Kea, removal of common mullein from experimental plots increased the cover of all grasses. Mauna Kea subalpine vegetation is species poor, and there are abundant bare sites. Grass cover was significantly greater (P<0.05) on sites where common mullein and associated litter were removed for all 3 years of the study. However, cover of forbs was lower in treatment plots, and by the third year of the study, forbs were significantly (P<0.05) lower on plots without common mullein. The presence of common mullein may have altered natural competitive interactions between grasses and forbs in this area [7]. Juvik and Juvik (as cited in [31]) suggest that grazing by feral sheep and goats in areas of Hawaii may have facilitated the establishment, spread, and persistence of common mullein in niches once occupied by the endangered Hawaii silversword (Argyroxiphium sandwicense subsp. sandwicense). Feral sheep and goats likely avoided common mullein in favor of other more palatable forage [31].
Control: Minimizing disturbances may be the most effective and economical method of common mullein control. Limiting open sites restricts common mullein's success. However, the very long-lived seed bank suggests that eradication of common mullein is unlikely, and even minimal disturbances may encourage common mullein establishment. In many areas, common mullein populations do not persist and abundance is dramatically reduced as time since disturbance increases. Potential control methods are discussed below.
Prevention: As a biennial species with a persistent seed bank, common mullein is adapted for widespread dispersal through time. The sudden appearance of common mullein is likely after disturbances expose buried seeds to light [13]. High levels of germination are possible in a wide range of temperatures, and germination percentages can be increased by 38% after only 5 seconds of light exposure [51].
Given the long-lived seed bank and wide range occupied by common mullein, transportion of soil may introduce or encourage common mullein establishment. Common mullein seedlings emerged from soil collected in a wetland constructed by a Department of Transportation mitigation project on New Jersey's Delaware River but did not emerge from soil taken from preexisting, nearby natural marshes [85].
Increased levels and frequencies of disturbances may increase the density of the common mullein seed bank. In northern Arizona, the density of common mullein seedlings emerging from soil samples increased with increased levels of past land use. There were 940 seedlings/m² in high disturbance areas and 566 seedlings/m² from areas with more moderate levels of disturbance [73].
Physical/mechanical: Physical control methods may be an effective method of removing small aboveground common mullein populations. Plants severed through the root crown below the basal leaves do not sprout [16]. Flowering stalks should be removed from the site to limit additions to the seed bank. In greenhouse experiments, common mullein did not survive defoliation in low-nitrogen environments [140].
Fire: See Fire Management Considerations.
Biological: There have been no purposeful introductions of common mullein biological control agents. In Europe, common mullein is most negatively affected by weevils (Gymnaetron tetrum) and mullein moths (Cucullia verbasci) [93]. Weevils were accidentally introduced in North America. Weevils can destroy all seeds within a capsule but rarely infest all capsules. Weevils may destroy up to 50% of common mullein seeds [16].
Chemical: Egler [42] reports that first year rosettes are easily killed by herbicide but that second year plants are more resistant. However, a review reports that common mullein's extreme hairiness reduces the effectiveness of herbicides. Aiming herbicides directly into the center of the rosette may increase herbicide effectiveness [16].
Integrated management: In the available literature, there was little mention of integrated management methods for common mullein. In a review by Reed [108], guidelines are provided for limiting the establishment and evaluating the potential impacts of nonnative and/or invasive species in restoration projects. Reed presents plans to limit and prepare for potential weedy species establishment as well as decision-making guidelines on whether to actively manage the weeds.
Deer, elk, mountain goats, and small mammals feed on common mullein. Deer and elk primarily utilize common mullein in the winter. Domestic grazing animals typically do not consume common mullein unless other forage is unavailable.
Elk and deer: Common mullein can be important in elk and deer winter diets. In South Dakota, researchers observed elk feeding on dry common mullein leaves when other forage was unavailable [64]. On the Threemile winter range in western Montana, the highest average relative density of common mullein in elk feces was 16.1% in January collections. Amounts of common mullein were much lower (0-2.2%) in December, February, March, and April [82].
On the Los Alamos National Laboratory in north-central New Mexico, common mullein was a predominant forage for deer in the winter and for elk in the fall and winter. Although common mullein had only trace cover in the study area, it made up 9% of elk and 7% of deer diets for all seasons evaluated over a 2-year period. Common mullein was 12% and 14% of fall and winter elk diets, respectively, and 17% of winter deer diets [117].
In Guadalupe Mountains National Park, Texas, researchers listed common mullein as 1 of 12 major mule deer food plants, although its average relative density was 1% of the annual diets [74]. On the Calf Creek winter range in western Montana, the greatest average relative density of common mullein was 2.5% in mule deer feces collections [82]. White-tailed deer in Michigan's Wilderness State Park defoliated common mullein rapidly after the first snow when the Park was near or over carrying capacity and winter food was "approaching a critical stage". White-tailed deer consumed common mullein leaves and chewed some flowering stalks [60].
Mountain goats: On Chopaka Mountain in north-central Washington, the high relative density of common mullein was 1.5% in summer-collected fecal samples. Over the 3-year period, the relative density of common mullein was lower, 0.1% to 0.3% in fall, winter, and spring samples. Mule deer or cattle fecal samples collected over a 2-year period contained no common mullein [21].
Small mammals: Common mullein is likely a food source for small mammals throughout its range, but studies and observations are generally lacking. In South Dakota, common mullein seeds and fruits provide food for chipmunks, prairie dogs, and other small mammals [64,69]. In Wind Cave National Park, South Dakota, researchers observed prairie dogs feeding on common mullein. Plants over 3 feet (1 m) tall were clipped by prairie dogs throughout the summer to maintain visibility in their town. Portions, likely fruits and seeds, were consumed, and the rest of the plant was "destroyed" [69].
Livestock: Livestock typically avoid common mullein (Isley, personal communication, cited in [52]). Some suggest that common mullein is poor forage and is "never grazed" [62,103]. In the mixed-conifer zone of California's Blodgett Forest Research Station, however, the abundance of common mullein in cow summer diets ranged from 0% to 3.5%. Fecal samples were collected for 2 years in an area stocked at 16 ha/AU [68].
Insects: Grasshoppers avoid feeding on common mullein's hairiest immature leaves. During field experiments in northern Arizona, young and immature leaves with the densest and longest hairs were fed on significantly less (P<0.001) than mature leaves [151].
Given a seed source and a canopy opening, common mullein is a potential
inhabitant of nearly any vegetation or community type. It has been described in
meadows, prairies, desert shrublands, chaparral, deciduous woodlands, and
coniferous forests throughout North America [16,32,123,135,152].
Common mullein typically produces ephemeral populations on disturbed sites.
Local extinction is common as succession progresses in most vegetation types.
Many common mullein studies have been conducted in abandoned agricultural fields.
Throughout this review, the age of old fields refers to time since abandonment or
time since last cultivation. For example, "1-year-old fields" have been
out of cultivation or left fallow for 1 year. In southwestern Michigan, common mullein
seedling establishment and survival was restricted to 1-year-old fields when seeds
were sown in both 1-year-old and 15-year-old fields [53]. Often common mullein is
not present in aboveground vegetation but appears soon after a disturbance. Establishment
on disturbed sites is most often the result of germination from a persistent seed bank.
These topics are discussed in more detail in Seed banking, Seedling establishment/growth, and Successional Status.
European cultures had a variety of uses for common mullein. These many uses likely encouraged the early transport and introduction of this species into nonnative areas. Parker [103] has aptly called common mullein "a waif of civilization". In as early as the 4th century BC, yellow common mullein flowers were used to dye hair [64]. Romans dipped flowering stalks in tallow and used them as torches [66]. In a review of folk medicine, common mullein was said to be used to treat respiratory disorders such as asthma, tuberculosis, bronchitis, and pneumonia; to combat tumor formation; and to treat urinary tract infections and skin diseases. Hemorrhoids, diarrhea, warts, migraines, frost bite, and ringworm were also treated with common mullein [137]. In Europe, concoctions of common mullein leaves and roots were used to treat many respiratory and alimentary conditions [10].
Native Americans also utilized common mullein. Southwestern tribes, including the Hopi, smoked dried common mullein leaves and flowers with giant-trumpets (Macromeria viridiflora) or other plants to treat mental illness [66,67]. Potawatomis, Mohegans, Penobscots, and Menominess smoked dried common mullein leaves to treat colds, bronchitis, and asthma. Catawbas made a cough syrup from boiled common mullein roots, and a poultice of mashed leaves was used to relieve bruises, wounds, and sprains. Choctaws used a poultice of leaves for headaches [10].
Early European settlers in the eastern United States used common mullein seed to sting or poison fish. Common mullein seeds were crushed and put into diked areas of slow moving water. Fish breathing was severely reduced or stopped by the toxic seeds. Fish "stings" were an easy method of food collection and often turned into community events. Sometime before the Revolutionary War, common mullein seeds were brought from Europe and cultivated for this purpose [148]. Colonial women rubbed common mullein leaves on their cheeks to redden them [146].
Today common mullein is one of several plants used in herbal ear drops used to treat earaches in children (>5 years) [119]. Common mullein leaves and flowers, capsules, alcohol extracts, and flower oil are available for medicinal use in the United States, and a recent (2002) study of common mullein extracts revealed antibacterial and antitumor properties [136,137]. In a Northwest floral guide, basal common mullein leaves are noted as potential insoles for weary hikers [104].
Common mullein rosettes often remain green through the winter [64]. Plants on a south-facing slope in Colorado's Gregory Canyon had high photosynthetic rates when leaves were sampled from 10 to 22 January [4]. Flower stalks often persist through the winter [64].
Southern common mullein populations flowered earlier and longer than northern populations when 24 populations from southern Canada, North Carolina, Texas, and Georgia were studied. A vernalization period was not required in southern populations [110].
Timing of common mullein development by state or region State/region Timing of reproductive development Arizona, north-central flowers mid-July to mid-September, seeds mid-October [25] California flowers June-September [97] Florida reproductive season summer-fall; flowers as early as June, fruits by September [27,153] Illinois flowers May-September [96] Kansas flowers June-September [10] Nevada flowers June-September [66] New York (Adirondack Uplands) flowers July-August [75] North and South Carolina flowers June-September [106] Texas flowers May-July, rarely later [36] Virginia flowers June-September [130] Atlantic and Gulf coasts flowers March-November [41] Blue Ridge Province flowers June-September [150] Eastern United States flowers June-September [45] Great Plains flowers June-July [47] Intermountain West flowers June-July [30] New England flowers middle July-middle August [121] Canada flowering begins late June, tall stalks may flower into late September, October [52] Nova Scotia flowers July-August [113]Germination of on-site seed is the predominant postfire regeneration method for common mullein. It is often present in the first postfire growing season, regardless of the timing of the fire. However, postfire emergence can be delayed and population persistence may be extended on sites burned in high-severity fires.
Seed survival: Common mullein seed in the soil is likely to survive and germinate after fire. However, high-severity fires with extended smoldering such as slash pile burns may kill a greater proportion of the common mullein seed bank [72,122]. In several studies, common mullein seedlings emerged from soils collected on burned sites. Emergence can be greater from soil samples collected on less severely [63] and less recently burned sites [125]. Yet germination from severely burned sites in the first postfire growing season is possible as well [63,122]. It is important to note that common mullein seed bank estimates can be affected by sample size, sample location, and experimental method. Abundant seed production and limited dispersal means that soil samples collected near or far away from a site once occupied by a prolific parent plant could affect findings [52,53,73].
Postfire establishment of common mullein may be delayed on some sites. Common mullein seedlings emerged from soil samples taken from 5-year-old burned but not from 1-year-old burned Douglas-fir forests in south-central British Columbia. Seedlings emerged from 7% of samples on 5-year-old burned sites and 41% of samples in 10-year-old clearcuts. On clearcut sites, common mullein's aboveground frequency was 6% [125]. Reasons for delayed postfire emergence are unknown. Severe fires likely consume more common mullein seeds since they typically consume the surface organic horizons. On less severely burned sites, it is possible that seed stored for an extended period in the mineral soil may require more time to germinate under field conditions. In a greenhouse study, dark germination of common mullein seed was lower after 2 years of burial than after 1 year of burial; researchers speculated that unknown factors associated with burial may prevent immediate germination [13]. A controlled study of the effects of heat on common mullein seed would improve the understanding of its seed bank dynamics on burned sites.
Common mullein emergence is sometimes lower on high-severity than low- or moderate-severity burned sites in the first 1 to 2 postfire growing seasons. Common mullein seedlings emerged from soils collected on low- and high-severity burned ponderosa pine forests in northern New Mexico's Rendija Canyon. The Cerro Grande fire burned in May 2000, and soil was collected in the fall of 2001. Forty-three, 0, and 1 seedlings emerged from plots sampled in low-, moderate-, and high-severity burned sites, respectively [63]. Common mullein was the dominant emergent from soil samples collected 10 feet (3 m) outside slash burn scars in ponderosa pine forests in Arizona's Coconino National Forest. Soil samples were taken 3 and 15 months after burning. There were 368 common mullein seedlings/m² in soil samples collected outside the burn scar. Density of common mullein from soil collected inside the scar was not given, but total seedling emergence (all species) from inside the scar was less than 50 emergents/m². These results suggest that some common mullein seed is killed by high-severity slash pile fires [72].
Fire may stimulate germination of common mullein seeds through chemical cues from smoke. Liquid smoke treatments increased common mullein emergence from soils collected in open-canopy ponderosa pine forests in northern Arizona. Common mullein averaged 35% frequency in the aboveground vegetation. Density of common mullein was 126 seedlings/m² in untreated soils and 252 seedlings/m² in soils treated with 60 mL of 10% liquid smoke [3].
Common mullein reproduces entirely by seed and has no means of vegetative regeneration [48].
Pollination and breeding system: Self and cross pollination of common mullein flowers are both possible. If by the end of the day an open flower has not been visited by a pollinator, it is self pollinated ("delayed selfing") [10,52]. While common mullein flowers are visited by a variety of insects, only short- and long-tongued bees are effective pollinators (Pennell 1935, cited in [52]), [22]. In field and greenhouse studies, researchers found that flowers fertilized by natural, delayed selfing set less seed than flowers that were outcrossed. Flowers pollinated by delayed selfing produced 75% of maximum fruit set. Delayed selfing may be important to small common mullein populations that may fail to attract pollinators [39].
Plant height likely affects pollinator visits and method of pollination. Taller plant heights significantly (P<0.02) increased outcrossing rates for 3 populations of common mullein in northeastern Georgia and southwestern North Carolina. Plants over 4.9 feet (1.5 m) tall experienced 21% more outcrossing than shorter plants [22]. Findings were similar for 6 common mullein populations near Kingston, Ontario. Significantly (P<0.0001) more pollen was deposited on tall plants with a median height of 5.6 feet (1.7 m) and an average of 13.5 flowers than on short plants with a median height of 2.6 feet (0.8 m) and an average of 5.5 flowers. Flowers at the top of an inflorescence also received significantly (P=0.0003) more pollen than flowers at the bottom [88]. Researchers in both studies concluded that taller plants attracted more pollinators than short ones [22,88].
Seed production: Common mullein produces abundant seed, and branching and fasciation of the flower stalk can lead to even greater seed production. In a 3-year-old abandoned field in Michigan, common mullein produced between 0 and 749 seeds/capsule for an average of 208 seeds/capsule. Total seeds per plant averaged 175,000 [52]. In 1- to 4-year-old fields in southwestern Michigan, common mullein averaged 100,000 seeds/plant [53]. An "average, well developed" common mullein plant in North Dakota, "growing with little competition" and sampled at a time when seed production was likely at a maximum, produced 223,200 seeds [127,128].
Studies have shown that common mullein rosettes must reach a minimum size before flowering. In a 4-year-old field in Kalamazoo County, Michigan, all rosettes greater than 6.1 inches (15.5 cm) in diameter flowered. In the greenhouse, however, rosettes beyond that size did not flower, suggesting a vernalization period may be necessary for flowering in temperate areas [49,54].
Branched inflorescences produced significantly (P<0.0001) more seeds than unbranched inflorescences in common mullein populations near Kingston, Ontario. The likelihood of branching increased significantly (P=0.0001) with plant height and decreased significantly (P=0.049) with population size. Branching was also associated with weevil damage. There was a significantly (P=0.0195) greater proportion of fruits damaged in branched plants [90].
While branching was affected by several factors, the reason for fasciation of common mullein spikes in Hawaii has not been determined. Ansari [7] found no difference between the prevalence of bacteria in normal and fasciated flowers, and physical damage to the flowering spike actually decreased fasciation rates. Evidence of single gene inheritance was also lacking, since there was no statistical difference in the prevalence of fasciation in normal and fasciated progeny [7]. Fasciated plants produced up to 3 times the seed of normal plants [33].
Seed dispersal: Common mullein seeds have no morphological adaptations for long-distance dispersal. Most seeds fall very near the parent plant [52,53]. Maximum dispersal distances of up to 36 feet (11 m) are possible, but the median dispersal distance is 3 feet (1 m) [52,54]. In natural settings, long-distance seed dispersal is rare. However, the long-lived common mullein seed bank makes transport of soil from areas where common mullein currently or historically occurred a potential long-distance dispersal event [16].
Seed banking: The common mullein seed bank is persistent. Seeds have germinated after 100 years or more in the soil [71,99]. The method used to determine seed bank composition and size, however, may affect common mullein seed bank findings. Seed bank estimates are much greater with the seedling emergence method than with the seed extraction method [19]. Seed bank estimates may also be affected by sample size and sample location. Because abundant common mullein seed is produced and dispersal is limited, soil samples collected near a site once occupied by a prolific parent plant could skew seed bank findings [52,53,73].
In Denmark, common mullein seed germinated from archaeological soil samples dated to 1300 AD [99]. In the late 1800s in Michigan, Dr. W J Beal buried seeds and soil in open jars about 3 feet (1 m) below the soil surface. Later jars were exhumed and germination of the soil samples was monitored in the greenhouse. Common mullein germinated from soil buried for 5, 15, 20, and 35 years [34]. Common mullein also germinated from soil buried 100 years [71]. In a similar study initiated by Dr Duvel in 1902, seeds were buried with soil in pots at increasing depths: 8 inches (20 cm), 22 inches (56 cm), and 42 inches (107 cm). Some common mullein seed germinated from all depths and from all periods tested between 1 and 21 years of burial. Germination percentages, however, were erratic and did not vary consistently with depth or length of burial [46]. After 39 years of burial, common mullein germination rates were 48% and 35% from 22 (56 cm)- and 42 (107 cm)-inch depths, respectively [133]. Seeds have also germinated at low percentages (3%) after 60 months in the water of Washington's Chandler Power Canal. Germination was much higher (82%) after 60 months of dry storage [28].
Methods of detection compared: Common mullein seed bank density estimates using the seed extraction method were much lower than those from the emergence method on soil samples collected in southern Ontario. Very small common mullein seeds were likely washed away or otherwise missed in the extraction method. Overall, the 2 methods provided very different pictures of the site's seed bank composition and density [19].
Frequency and density of common mullein seed in soil collected from a 2-year-old woodland clearcut in southern Ontario using extraction and emergence methods [19] Method Frequency (%) Density Seed extraction 6 87 seeds/m² Seedling emergence 90 1,299 emergents/m²Vegetation types compared: In most seed bank studies, common mullein was either absent or present at very low densities in the aboveground vegetation but still predominant in the seed bank. The common mullein seed bank can vary by vegetation type; however, patterns of variation are not consistent. It is likely that the soil area sampled and past land use are more important than current vegetation type. This idea is also discussed in Impacts and Control.
Common mullein seeds emerged from soil samples collected from 5 different vegetation types in the Mt Trumbull and Mt Logan Wilderness Areas of northern Arizona. Emergence was greatest from sites dominated by New Mexico locust (Robinia neomexicana) and lowest from sites dominated by old-growth ponderosa pine (Pinus ponderosa). Soil samples were collected in mid-September [123].
Common mullein seedling emergence from various vegetation types in northern Arizona [123] Canopy type Old-growth ponderosa pine Dense, pole-sized ponderosa pine Gambel oakOn limestone soils in Pennsylvania, common mullein seedlings emerged from soil samples taken from prairie, ecotone, and deciduous forest types. Common mullein was not present in the aboveground vegetation but emerged from 7 of 20 prairie, 6 of 20 ecotone, and 2 of 20 forest soil samples [81]. In the southern Appalachians, common mullein did not emerge from soil samples taken from a floodplain dominated by sedges (Carex spp.) or from soils taken from an adjacent site dominated by sapling red maple (Acer rubrum). A single common mullein seedling germinated from soil collected in a closed-canopy red maple forest [114].
Shrub-steppe: On ungrazed to heavily grazed areas dominated by antelope bitterbrush (Purshia tridentata) in the Okanagen Valley of British Columbia, common mullein occurred with much greater density in aboveground vegetation than in the seed bank. Aboveground density was 65 plants/m², while seed bank density was 0.2 seeds/m² [26]. It is important to note that researchers used the seed extraction method to characterize the seed bank. This method has been shown to underestimate common mullein seed abundance [19].
Coniferous forest: From 47-year-old loblolly pine (Pinus taeda) plantations in North Carolina, 840 common mullein seedlings/m² emerged from soil collections. The researcher noted that common mullein likely had not been present on the sites since canopy development [109]. The density of common mullein seedlings emerging from open-canopy ponderosa pine forests in northern Arizona was staggering. At depths up to 2 inches (5 cm), 4583 seedlings/m² emerged, and from 2- to 4-inch (5-10 cm) depths, 2,083 seedlings/m² emerged. Common mullein occurred in aboveground vegetation with an average frequency of 35% [3].
Deciduous forest: Common mullein seedlings emerged from soil collected in 6 of 8 deciduous forests in Tennessee's Anderson and Campbell counties. Stands were over 47 years old, and common mullein was not present in aboveground vegetation. Seedling density was greatest (93 seedlings/m²) in soil collected from yellow-poplar (Liriodendron tulipifera)-dominated sites, and the greatest abundance of common mullein seedlings came from 2- to 4-inch (5-10 cm) depths [37]. In 70- to 90-year-old mixed deciduous stands in the Yale-Myers Forest of northeastern Connecticut, common mullein seedlings emerged from mineral soil samples taken from midslope (33/m²) and ridgetop (17/m²) positions but not from valley sites. Soil samples to were taken to a depth of 2 inches (5 cm) [9].
Germination: Light and warm temperatures produce the greatest common mullein germination rates; however, some germination is possible in the dark and at burial depths of 1.1 inches (3 cm). Common mullein seeds are either nondormant or conditionally dormant. Seed collected from temperate climates is typically not dormant when temperatures are cool, but as temperatures increase, seeds show conditional dormancy or a narrowed range of suitable conditions for germination (Baskin and Baskin, cited in [12]).
Light, temperature and seed size: Common mullein seed germinates best with exposure to full light and warm temperatures, but several studies have shown that seeds exposed to cool or hot temperatures, drastically fluctuating temperatures, dark conditions, and very brief light exposure may also germinate. Soil disturbances can expose common mullein seeds to the light and increase germination. For more information, see Impacts and Control.
Seed size can also affect germination. Smaller common mullein seeds collected from old fields and roadsides of Michigan and Ohio had significantly (P<0.05) lower germination than medium and large seeds. Small seeds had the lowest and large seeds had the highest germination rates in both light and dark conditions [50].
Germination of small-, medium-, and large-sized common mullein seeds after 3 weeks in greenhouse [50] Seed size Average seed weight (mg) Percent germination in light Percent germination in dark Small 0.041 71.2% 19.2% Medium 0.056 90.4% 26.4% Large 0.070 92.8% 35.2%Germination of common mullein seed is generally low in dark conditions, but increased temperatures may improve dark germination. In the laboratory, newly harvested common mullein seeds collected from the University of Michigan's Botanical Gardens germinated at over 90% in the light and about 2% in the dark. Older seeds were also light sensitive. When seeds were in soil or sand, germination in dark conditions was better, 24% to 34% [44]. No common mullein seeds collected from 2-year-old fields in southwestern Michigan germinated in the dark. However, germination increased to 38% after 5 seconds of light exposure; after 30 seconds of light exposure, germination increased to 63%, which was not statistically different from germination in full light [51]. Temperature affected successful germination in a dark germinator. Germination was very low in sustained cold temperatures but increased some when fluctuating temperatures reached highs of 68 °F (20 °C) or more [101]. When controlled studies were conducted on common mullein seed collected from low- and high-elevation roadside sites in western Nevada and northern California, germination percentages reached a high of 98% in the dark at alternating warm temperatures of 77 and 95 °F (25/35 °C). In the light, common mullein seed germinated at constant 104 °F (40 °C) and at alternating 0 and 104 °F (0/40 °C) temperatures [120].
Using field and greenhouse studies, researchers concluded that common mullein seed germination is possible throughout most of the year in light conditions. Seed was collected in early September from Wilson County, Tennessee, buried under 2.8 inches (7 cm) of soil in Lexington, Kentucky, for 1 to 25 months, and exhumed at monthly intervals. Germination rates of fresh-harvested seed were 0% at alternating temperatures of 56 °F and 43 °F (15/6 °C), 8% at 68/50 °F (20/10 °C), 97% at 86/56 °F (30/15 °C), and 95% at 95/68 °F (35/20 °C). Germination rates varied with season. Seeds removed in the winter had lower temperature requirements for germination. At high temperatures, 10% of seeds germinated in dark conditions, while none germinated in the dark at low temperatures [13].
Burial/canopy cover: Common mullein seed germinates best on the soil surface in areas with low canopy cover. Germination success generally decreases with increased depth of burial and increased canopy cover.
Emergence of common mullein in established Kentucky bluegrass (Poa pratensis) was significantly lower than emergence in litter or bare soil (P<0.0001). In litter or bare soil, emergence of common mullein was rapid and synchronous, and nearly 50% of maximum emergence occurred within 15 days of being sown [50]. Seed collected from 2-year-old fields in southwestern Michigan germinated at much lower percentages under a simulated canopy than under full light conditions [51]. After 2,500 seeds were sown in 1-year-old, 5-year-old, and 15-year-old fields at the W K Kellogg Biological Station, Michigan, common mullein emergence was greatest in 1-year-old fields with the greatest amount of bare ground. Survival of seedlings was evaluated in 1-year-old and 15-year-old fields; results are presented in Seedling establishment/growth below [53,54].
Seedling emergence with increasing field age and decreasing bare ground availability [53,54] Field age Percentage of bare ground Number of seedlings emerged 1 year 66 20.85a 5 years 10.8 6.3b 15 years <1 2.75b Emergence values followed by different letters are significantly different (P<0.05)Factors other than darkness associated with burial may prevent germination. Using field and greenhouse studies, researchers found that fewer common mullein seeds germinated in the dark at spring temperatures after 2 years of burial than after 1 year of burial [13]. Common mullein seeds collected from northern California roadsides and tested in a greenhouse study germinated better under a litter layer than under a soil layer, and increasing depth of burial corresponded to decreased germination percentages [120].
Percentage of common mullein germination with increasing depth of burial [120] Burial depth (cm) Seed source Sierra County, CA Lassen County, CA Donner Summit, CA Elevation: 1,510 mSeedling establishment/growth: Predictions regarding common mullein's survival and flowering success can be made by measuring its rosette size. Successful establishment and rosette size are affected by site conditions and the availability of open sites.
Probability of common mullein survival and flowering generally increase as rosette size increases. In 4-year-old fields in Kalamazoo, Michigan, rosettes less than 3.5 inches (9 cm) in diameter failed to flower in the subsequent year, but all those greater than 16 inches (41 cm) flowered. Of the 1,006 plants studied, very few survived more than 2 years, and none survived more than 3 years [49]. Probability of dying or not flowering was greatest for small-sized rosettes in 24 common mullein populations from southern Canada, North Carolina, Texas, and Georgia. Very large rosettes over 28 inches (70 cm) in diameter also had a lower probability of survival than those of intermediate diameter. As latitude of the population increased, so did the likelihood that plants with small rosettes would remain vegetative (P<0.001) [110]. Findings were similar on Mauna Kea in Hawaii. Common mullein's probability of dying without flowering decreased and probability of flowering increased with increasing rosette size, which was typically greatest at the highest elevation sites. Rosettes over 10 inches (25.5 cm) in diameter had a 0.08 probability of dying, a 0.15 probability of remaining vegetative, and a 0.77 probability of flowering [7].
Emergence timing may or may not affect common mullein germination, rosette size, flowering, or survival. At sites ranging from 5,540 to 8,860 feet (1,690-2,700 m) elevation on Mauna Kea, common mullein survival and reproductive success were not affected by timing of cohort emergence [7], but timing of cohort emergence was critical to common mullein's survival and reproductive success in southwestern Michigan [48]. The fate of more than 7,000 common mullein seedlings was monitored for 3 years on the island of Hawaii. There were 4 emergence cohorts, but timing of emergence did not affect germination, rosette size, flowering, or survival. Some variation appeared to be related to elevation. Seedling density, rosette diameter, and leaf number were greater at high-elevation sites than at low-elevation sites, which had greater precipitation and more associated vegetation. However, probability of flowering was greatest at the lowest elevation sites. The proportion of plants that delayed flowering beyond 2 years of age was greatest at high-elevation sites [7].
Common mullein seedlings emerged in mid-May, mid-June, and mid-August, generally after 3 to 4 days of rain, in a 3-year-old field at Michigan's W K Kellogg Biological Station. None of the seedlings that emerged in August, the largest cohort, survived the winter. When neighboring vegetation was removed, survival increased [48].
Fate of common mullein plants with timing of emergence in a 3-year-old field in Michigan [48] Cohort Number of seedlings Probability of surviving winter Number of flowering plants Mean height of flowering plants (cm) Mean number of seeds/plant Overall probability of reproducing May 116 0.50 4 92.1 2,050 0.035 June 2,640 0.75 6 38.1 380 0.003 August 29,060 0 0 0 0 0.000Open site availability: Like seed germination, common mullein seedling establishment is best on open sites. Time since disturbance and its relationship to open-site availability affects seedling size, survival, and reproductive success. Seedling growth was dramatically lower when seeds were sown in containers with established Kentucky bluegrass than when planted in litter or bare soil [50].
Final average dry mass (mg) of common mullein seedlings* in containers with bare soil, litter, or established Kentucky bluegrass [50] Bare soil Litter Kentucky bluegrass Kentucky bluegrass and litter 874-1,013 1,003-1,147 0.07-0.22 0.09-0.16 *First number is average for seedlings from small-sized seeds; last number is average for seedlings from large-sized seeds.In southwestern Michigan, common mullein seedlings established and survived only in 1-year-old fields when seeds were sown in 1- and 15-year-old fields. Seedlings that survived to the end of the growing season (~20 weeks) on 1-year-old fields were restricted to bare areas. When openings were created in 15-year-old fields, seedling emergence increased and some seedlings established [53,54].
Decreased germination, lower survival, and delayed reproduction were typical in common mullein populations in North Carolina's Piedmont as time since disturbance increased. Common mullein seedlings that established 2 to 3 years after a disturbance had a greater chance of remaining vegetative in their 2nd year than those established in the 1st postdisturbance year. When areas were artificially disturbed, seedlings had a high probability of flowering in their 2nd year. The researcher concluded that the "successional age of the habitat determined the relative fitness of the biennial and triennial plants" [112].
Seedling density and seedling survival with increasing time since disturbance. Ranges include information from 2 to 6 common mullein populations [112] Time since disturbance (years) 1 2 3 Seedlings/m² 98.9-127.6 0-14.1 0-3.8 Fraction of seed pool germinating (%) 11.2-26.6 0-2.9 0-0.02 Seedlings surviving to end of 1st growing season (%) 14.9-17.8 0-2.5 0-7.1Vegetative regeneration: Common mullein has no means of vegetative regeneration [48].
Common mullein is an early-seral species. On disturbed sites, common mullein emerges from soil-stored seed. Common mullein rarely persists beyond the first few postdisturbance years. However, in some meadows of California and sparsely vegetated alpine sites in Hawaii, common mullein is not restricted to disturbed sites and has not been replaced in natural succession. For more on these exceptions, see Impacts and Control.
Rarely is common mullein described in undisturbed communities. The creation of sunny, open sites by heavy grazing, severe storms, logging, fire, or other disturbances is generally necessary for common mullein establishment, growth, and reproductive success. On south-facing slopes of Gregory Canyon near Boulder, Colorado, common mullein did not grow on "deeply-shaded sites" [4]. Even large-sized common mullein plants typically die or fail to reproduce on shaded sites (Reinartz, unpublished data cited in [110]). In West Yellowstone, common mullein was found only at sites with less than 30% canopy cover, and most occurrences (75%) were at sites with ≤5% canopy cover [6]. In coastal upland habitats of southern New England and adjacent New York, common mullein occurred only on open plots and not on any of the 56 heath-dominated, 175 shrubland, or 446 forested plots [142].
Postdisturbance common mullein populations are typically ephemeral, and as time since disturbance increases, common mullein abundance normally decreases. Old-field succession was evaluated on many sites in southwestern Michigan. Common mullein was often abundant only in fields less than 5 years old [53]. Common mullein established from long-lived seeds present in the seed bank at the time of disturbance. As time since disturbance increased, the proportion of open space decreased as did the probability of successful establishment. In old fields, local common mullein extinctions are rapid, but long-lived, soil-stored seed emergence is likely with the next disturbances [48,54]. Common mullein populations in southern Canada, North Carolina, Texas, and Georgia rarely persisted more than 4 years after disturbance. Of the 24 populations monitored, only 2 had germination in the year after initial postdisturbance population establishment [110].
Vegetation type and disturbance severity may affect the persistence of common mullein in early-seral communities. In the Yale-Myers Forest of northeastern Connecticut, common mullein was present the first year after all vegetation was removed from 85-year-old northern red oak (Q. rubra) stands but was not present the third year after vegetation removal. On sites where only the canopy was removed, common mullein did not occur [5]. In ponderosa pine forests of the Southwest, common mullein may occur in low abundance up to 30 years after severe fire [14].
Grazing: Common mullein is often described on severely grazed sites. In British Columbia and Montana rangelands, common mullein does not normally occur in "climax" grasslands, but its abundance increases as range condition deteriorates [77,94]. In southwestern Utah, common mullein was one of several species noted on "depleted," "severely grazed" Gambel oak types [18]. On overgrazed sties in South Dakota, common mullein is "especially prevalent" and "extremely abundant" [64]. In Wisconsin's Coon Valley, common mullein often appears when there is grazing in black oak (Q. velutina) communities [91]. Common mullein is also common on heavily grazed cleared forests and bluegrass grasslands attacked by June beetle larvae. In these areas, the tall weedy forb community can become an "impenetrable jungle-like thicket 4 to 7 feet (1.2-2 m) tall" [32].
While increased abundance of common mullein on grazed sites is normal, on the Blandy Experimental Farm in Virginia, common mullein decreased more rapidly on old fields with herbivore pressure than on those without. Direct use of common mullein by the grazers was not evaluated, and consumption of seeds or plants may have affected results [17].
Change in percent cover with time and herbivore exclusion treatments in Virginia [17] Time span ControlStorms: Severe storm events that cause tree mortality and create canopy openings provide early-seral habitat for common mullein. Four years after Hurricane Fran (1996), common mullein occurred in plots that were damaged on North Carolina's Duke University Forest. The hurricane created patchy forest openings [132]. In Minnesota's Cedar Creek Natural History Area, common mullein frequency ranged from 2.2% to 42% in areas where eastern white pine (Pinus strobus) trees were uprooted by a July windstorm that reduced tree density from 1,104 to 446 trees/ha. Fourteen years after the storm, common mullein frequency still ranged from 3.8% to 16.1% [100].
Logging and fire: Common mullein frequently occupies newly cut forest sites throughout its range. Common mullein was abundant in the first year after 100-year-old eastern white pine stands were clearcut in northwestern Connecticut. Sites were bulldozed following cutting to expose mineral soil. There were over 100 common mullein plants on the two 5,000 m² treated plots [35]. Common mullein frequency was 23% three years after a mixed-conifer forest was clearcut and burned in northeastern Oregon's Wallowa Mountains. By 14 years after the treatment, common mullein frequency was reduced to 3% or less [95]. In ponderosa pine forests on Mt Trumbull in northern Arizona, common mullein occurred on skid trails and in areas where slash was piled during a thinning operation. Common mullein did not occur on undisturbed sites, and density on treated sites averaged 2.9 plants/m² [123].
Common mullein frequency increased with increasing intensity of cutting in ponderosa pine forests on Arizona's Coconino National Forest. Common mullein frequency was greatest on sites with the greatest tree reduction. Common mullein frequency increased from the 3rd to the 6th posttreatment year on the most heavily thinned plots. Thinned sites were also burned in strip head fires [1,2].
Frequency of common mullein with increased intensity of thinning of ponderosa pine forests [1] Treatment intensity Pretreatment density of ponderosa pine (trees/ha) Posttreatment density of ponderosa pine (trees/ha) Frequency of common mullein (%) 3 years after treatments Frequency of common mullein (%) 6 years after treatments [2] Control 1,188 1,188 0 0 Low 1,044 243 <1 no data Medium 1,492 170 12 11 High 956 140 14 56On the same sites discussed above, researchers experimentally scarified soils with increasing intensity and evaluated common mullein frequency. On unthinned plots, soil disturbance was followed by little change (≤6%) in common mullein frequency. On thinned plots common mullein frequency increased 0% to 28% after soil disturbance [2].
Frequency of common mullein was much greater on bulldozed than burned sites after a severe fire in alvar woodlands near Ottawa, Ontario. Common mullein frequency was 8% fifteen months after the fire. In the bulldozed area of the adjacent unburned site, the frequency of common mullein was 50% [23,24].
For more on common mullein and fire, see Fire Effects.
The scientific name of common mullein is Verbascum thapsus L. (Scrophulariaceae)
[47,58,65,144,153].
Hybridization occurs within the genus. Common mullein ÃÂ white mullein (V. lychnitis)
hybrids are suspected in Michigan [143], and common mullein ÃÂ orange mullein (V. phlomoides)
hybrids, V. ÃÂ kerneri Fritsch, occur in the Northeast [45].
