Invasiveness Assessment - Illyrian thistle (Onopordum illyricum) 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 Illyrian 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)
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Common Name: Illyrian thistle
Scientific name: Onopordum illyricum
| Question | Comments | Reference | Rating |
| Establishment | |||
| Germination requirements? | “Seeds may germinate at any time of the year but most do so after autumn rains”. | P & C (1992) | H |
| Establishment requirements? | Mostly establishes in ‘open’ habitats, e.g. pastures. | P & C (1992) | ML |
| How much disturbance is required? | Establishes in vigorously growing pastures. (See pic. P & C 1992 p. 222). | P & C (1992) | MH |
| Growth/Competitive | |||
| Life form? | Erect annual or biennial herb. Other. | P & C (1992) | L |
| Allelopathic properties? | None described |  | L |
| Tolerates herb pressure? | Not grazed by stock because of the dense spines. Consumed by (sheep and goats), however still capable of propagule production. | P & C (1992) Campbell & Holst (1990) | MH |
| Normal growth rate? | Competitive in pastures. Described as a ‘rapid spreader’. (Anon.) | P & C (1992) | MH |
| Stress tolerance to frost, drought, w/logg, sal. etc? | Tolerant of drought. | Pettit et al (1996) | L |
| Reproduction | |||
| Reproductive system | Reproducing by seed. “Cultivation can spread root pieces which may grow”. “Onopordum thistles are not capable of vegetative reproduction”. (Pettit et al 1996). | P & C (1992) ACT Parks & Conservation Service | ML |
| Number of propagules produced? | “A heavy seeder”. (Anon). 5 flower heads per plant x 200 seeds per flower = 1,000 seeds per plant (Estimate using pic. & illustrations) | P & C (1992) ACT Parks & Conservation Service | MH |
| Propagule longevity? | > 6 years (See Sindel 1997 p. 2). However unsure if large/small % are viable > 6 years. | Sindel (1997) | ML |
| Reproductive period? | Annual or biennial. “Some plants develop flowering stems in the first spring, whilst others do not flower until the second spring”. Therefore only produces propagules for 1 year. . | P & C (1992) | L |
| Time to reproductive maturity? | Some plants flower in the first year, others in the second year. | P & C (1992) | H |
| Dispersal | |||
| Number of mechanisms? | Wind; contaminate wool, other agricultural produce and equipment. Also spread by water. | P & C (1992) | MH |
| How far do they disperse? | “The pappus of the seed attaches to wool, vehicles, clothing, etc or it can be a contaminant in hay. The stems with seed heads attached can break off and be blown some distance “. (ACT Parks & Conservation Service). Above mechanisms, particularly seed attaching to wool, vehicles and clothing could be transported well > 200 m. | P & C (1992) | MH |
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