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Invasiveness Assessment - Great Mullein (Verbascum thapsus) in Victoria (Nox)

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Plant invasiveness is determined by evaluating a plant’s biological and ecological characteristics against criteria that encompass establishment requirements, growth rate and competitive ability, methods of reproduction, and dispersal mechanisms.

Each characteristic, or criterion, is assessed against a list of intensity ratings. Depending upon information found, a rating of Low, Medium Low, Medium High or High is assigned to that criterion. Where no data is available to answer a criterion, a rating of medium (M) is applied. A description of the invasiveness criteria and intensity ratings used in this process can be viewed here.

The following table provides information on the invasiveness of Great mullein.

A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:

Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1 MB)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).

Common Name: Great mullein
Scientific name: Verbascum thapsus

Question
Comments
Reference
Rating
Establishment
Germination requirements?Seeds germinate in autumn and spring”.
P & C (1992 p. 587)
MH
Establishment requirements?Establishes in open habitats and ecosystems e.g. areas of abandoned cultivation.
P & C (1992 p. 587)
ML
How much disturbance is required?Invades undisturbed ecosystems (e.g. alpine and sub-alpine vegetation).
Carr et al (1992)
H
Growth/Competitive
Life form?Erect biennial herb.

Other.
P & C (1992 p. 586)
L
Allelopathic properties?“Allelopathic effects have been reported on wheat seedlings but this is not a practical problem because the plant is not a weed of cereal crops”.
P & C (1992 p. 588)
ML
Tolerates herb pressure?“The rosettes, which cover a large area, are rarely eaten by livestock”.
P & C (1992 p. 587)
MH
Normal growth rate?“It prefers disturbed habitats with little other vegetation”.

“It is easily crowded out by grasses or other competing vegetation”.
Bassard et al (2000 p. 322/23)
ML
Stress tolerance to frost, drought, w/logg, sal. etc?Tolerant of frost (occurs in southern Tasmania); drought (occurs in central New South Wales and Western Australia). Occurs in ‘moist meadows and drainage’s’ in California.
P & C (1992 p. 586)
Bassard et al (2000 p. 323)
MH
Reproduction
Reproductive system“Reproducing by seed”.

“Flowers are autogamous, that is they self-pollinate if cross-pollination does not occur’.
P & C (1992 p. 586/87)
ML
Number of propagules produced?“Single plants produce 200 to 300 capsuled with 500 to 800 seeds per capsule. This seed production can be 100,000 to 240,000 seeds per plant”.
Bassard et al (2000 p. 323)
H
Propagule longevity?“In Denmark, seeds recovered from soil samples claimed to be more than 650 years old were viable”.
P & C (1992 p. 587)
H
Reproductive period?“Most plants are biennial but occasionally they can be annual or short lived perennials”.
P & C (1992 p. 587)
L
Time to reproductive maturity?“Plants usually bolt, flowering stem, in the second year and have a single stem covered with over lapping; woolly leaves from base to inflorescence”.
Bassard et al (2000 p. 322)
MH
Dispersal
Number of mechanisms?“Seeds are not adapted to dispersal by wind or animals and usually fall to the ground. Field studies report that seeds will disperse as far as eleven metres, but 75% fall within one metre of the parent plant”. “Most seeds fall within 1.5 metres of the parent plant when it is moved by wind or large animals.
MH
How far do they disperse?
Bassard et al (200 p. 322)
P & C (1992 p. 587)
L


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