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Invasiveness Assessment - Thistle (Onopordum dissectum) in Victoria
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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 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 - 1026 KB)
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Common Name: Thistle
Scientific name: Onopordum dissectum
| Question | Comments | Confidence | Rating |
| Establishment | |||
| Germination requirements? | “Plants typically germinate in fall [autumn] after first rains” (Healy, Enloe & DiTomaso, 2005). | MH | MH |
| Establishment requirements? | Most species grow in rocky or stony ground, roadsides, waste places and similar dry, open habitats (Tutin, 1993). Onopordum in general grow along roadsides and in fields (Healy, Enloe & DiTomaso, 2005). Requires open space. | ML | MH |
| How much disturbance is required? | Most species grow in rocky or stony ground, roadsides, waste places and similar dry, open habitats (Tutin, 1993). Onopordum in general grow along roadsides and in fields (Healy, Enloe & DiTomaso, 2005). Establishes in highly disturbed ecosystems. | ML | MH |
| Growth/Competitive | |||
| Life form? | Biennial (Tutin, 1993). | L | MH |
| Allelopathic properties? | No information found. | M | L |
| Tolerates herb pressure? | For all Onopordum, stems spinose-winged, or absent…involucral bracts spine-tipped (Tutin, 1993). Spines on the inflorescence (and probably the stems) would deter herbivory by vertebrates. | MH | MH |
| Normal growth rate? | No information found. | M | L |
| Stress tolerance to frost, drought, w/logg, sal. etc? | Grows in deep dry soils in Spain and Portugal (Rivas-Martinez et al, 2002). No further information found about stress tolerances. | M | L |
| Reproduction | |||
| Reproductive system | Onopordum reproduce only by seeds (Healy et al, 2005). No further information found. | ML | L |
| Number of propagules produced? | Average of 218 capitula per plant (Briese et al, 1995).No further information found. | M | L |
| Propagule longevity? | No information found. | M | L |
| Reproductive period? | “Flowering stems develop during the second spring/summer season” (Healy, Enloe & DiTomaso, 2005) on this biennial plant (Tutin, 1993), so that they produce seed for only one year. | L | MH |
| Time to reproductive maturity? | Biennial (Tutin, 1993). “Flowering stems develop during the second spring/summer season” (Healy, Enloe & DiTomaso, 2005), within two years of germinating. | MH | MH |
| Dispersal | |||
| Number of mechanisms? | No information found. | M | L |
| How far do they disperse? | No information found. | M | L |
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