Invasiveness Assessment - Cotton thistle (Onopordum nervosum) in Victoria

Back | Table | Feedback

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 Cotton thistle.

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: Cotton thistle
Scientific name: Onopordum nervosum

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	Its vegetative cycle starts in Autumn (Manzanares et al, 1993). Requires natural seasonal disturbances.	MH	H
Establishment requirements?	Grows in rocky or stony ground, roadsides, waste places and similar dry, open habitats (Tutin, 1980). Requires open space to establish.	MH	MH
How much disturbance is required?	Grows in rocky or stony ground, roadsides, waste places and similar dry, open habitats (Tutin, 1980). Establishes in highly disturbed ecosystems.	ML	MH
Growth/Competitive
Life form?	Biennial (Tutin, 1980).	L	MH
Allelopathic properties?	None found, but there is very little information about this species.	M	L
Tolerates herb pressure?	Leaves and stems bear spines up to 1 cm long (Tutin, 1980), which would deter most vertebrates, except perhaps for goats who eat the seed heads of the related O. illyricum (Holst & Allan, 1996). Weevils were introduced to Australia to control this genus in 1992, but it was found that less than 20% of O. tauricum capitula were attacked (Briese, 2000). These thistles are still capable of seed production under most herbivory pressure.	MH	MH
Normal growth rate?	No information found.	M	L
Stress tolerance to frost, drought, w/logg, sal. etc?	Grows in dry habitats (Tutin, 1980). No further information about tolerances found.	M	L
Reproduction
Reproductive system	Onopordum reproduce only by seeds (Healy, Enloe & DiTomaso, 2005). No further information found.	M	L
Number of propagules produced?	Average of 218 capitula per plant (Briese et al, 1995). Each capitualum appears composed of over 100 florets (see picture in ENG, 2002). 218 x 100 = 21 800.	H	ML
Propagule longevity?	“Buried seed [of Onopordum spp.] may persist for up to twenty years” (Healy, Enloe & DiTomaso, 2005). Deep dormancy has been observed in O. nervosum seeds (Perez-Garcia & Duran, 1990).	H	H
Reproductive period?	Biannual plant. Its vegetative cycle starts in Autumn…ending the cycle in summer with flowering and fructification (Manzanares et al, 1993). Produces propagules for more than one year but less than two.	ML	H
Time to reproductive maturity?	Its vegetative cycle starts in Autumn…ending the cycle in summer with flowering and fructification (Manzanares et al, 1993). Produces seed in less than one year.	H	H
Dispersal
Number of mechanisms?	No information found.	M	L
How far do they disperse?	No information found.	M	L

Feedback

Do you have additional information about this plant that will improve the quality of the assessment?
If so, we would value your contribution. Click on the link to go to the feedback form.

Page top