Invasiveness Assessment - Slender thistle (Carduus pycnocephalus) 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 Slender 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: Slender thistle
Scientific name: Carduus pycnocephalus
| Question | Comments | Reference | Rating |
| Establishment | |||
| Germination requirements? | Seed germinates after autumn rains. | P&C (1992) | MH |
| Establishment requirements? | Can establish under shading. | Mar Anon & Bartolome (1993) | MH |
| How much disturbance is required? | Serious environmental weed in woodlands, riparian veg., rainforest etc. | Carr et al (1992) | MH |
| Growth/Competitive | |||
| Life form? | Erect annual herb - ‘Other’. | P&C (1992) | L |
| Allelopathic properties? | None described. |  | L |
| Tolerates herb pressure? | Not readily grazed by stock b/c of its spiny nature. | P&C (1992) | MH |
| Normal growth rate? | More competitive than subterranean clover & ryegrass over a wide range of nutrient levels. | P&C (1992) | MH |
| Stress tolerance to frost, drought, w/logg, sal. etc? | Tolerant of waterlogging (grows on creek banks), salinity (occurs in coastal areas), drought. | K&J (1977) Clapham et al (1952) Carr et al (1992) Pitcher & Russo (1995) | MH |
| Reproduction | |||
| Reproductive system | Reproducing by seed. (Self & cross pollination assumed). As there is much information on this plant, the literature would have probably stated if only one self or cross pollinated. | P&C (1992) | ML |
| Number of propagules produced? | According to one study approx. 833 seeds produced/plant. | Goeden & Ricker (1985) | ML |
| Propagule longevity? | Most seeds germinate in the autumn after they are produced but some may remain dormant for at least 10 years. Short-term innate dormancy (several weeks to months) has been established for seeds of some thistles under certain conditions, e.g. pycnocephalus & C. tenuiflorus. (Sindel 1991). The length of time the seeds can survive in the soil is not known but appears to be at least 8 years (Parsons 1973) (Pitcher & Russo 1995). | P&C (1992) | L |
| Reproductive period? | Form dense populations → monocultures. | Bendall (1973) | H |
| Time to reproductive maturity? | Annual. | P&C (1992) | H |
| Dispersal | |||
| Number of mechanisms? | Wind dispersal, animals, birds; pasture seed, contaminated by hay & water. | P&C (1992) | H |
| How far do they disperse? | Several birds eat the seeds. The distance that seed can be spread by wind is not known, but is at least several hundred metres (Pitcher & Russo 1995). | P&C (1992) | H |
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