Invasiveness Assessment - Star thistle (Centaurea calcitrapa) 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 Star 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: Star thistle
Scientific name: Centaurea calcitrapa
| Question | Comments | Reference | Rating |
| Establishment | |||
| Germination requirements? | Some seeds germinate at any time of the year if moisture is available, however, most germ occurs after the autumn break. | P&C (1992) | H |
| Establishment requirements? | Mostly occurs in ‘open, unshaded situations’. | P&C (1992) | ML |
| How much disturbance is required? | An environmental weed in grasslands, grassy woodlands, dry sclerophyll forest & woodlands. | Carr et al (1992) | MH |
| Growth/Competitive | |||
| Life form? | An erect annual or biennial herb → ‘Other’. | P&C (1992) | L |
| Allelopathic properties? | None described. |  | L |
| Tolerates herb pressure? | May be consumed, but not preferred due to the presence of spines that injure grazing animals. | P&C (1992) | MH |
| Normal growth rate? | Competes with crops & pastures. | P&C (1992) | MH |
| Stress tolerance to frost, drought, w/logg, sal. etc? | Tolerance to drought. | S&B (1996) H&M (1983) | L |
| Reproduction | |||
| Reproductive system | Reproducing by seed. | P&C (1992) | ML |
| Number of propagules produced? | Flower heads are numerous. (Using pictures – NSW Dept Ag (1962) & P&C (1992) no. of propagules./plant was estimated. 50 flowering heads x 20 flowers/head x 1 seed/flower = 1,000 seeds/plant. | NSW Dept Ag (1962) | MH |
| Propagule longevity? | Seed is relatively short-lived, surviving for only 2-3 years in soil. | P&C (1992) | L |
| Reproductive period? | Forms dense masses of growth. Wide spread, medium to large population. | NSW Dept Ag (1962) Carr et al (1992) | H |
| Time to reproductive maturity? | Mostly annual, sometimes biennial. | P&C (1992) | H |
| Dispersal | |||
| Number of mechanisms? | Spread to some extent by water along channels & by contaminating agricultural produce, equipment etc. Also by wind. | P&C (1992) | MH |
| How far do they disperse? | Lacking long-distance dispersal mechanisms. Most effective means probably ‘tumbleweed’ mechanism | P&C (1992) | L |
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