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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. |
Question | Comments | Reference | Rating |
Establishment | |||
Germination requirements? | “Seeds germinate in autumn, winter and spring”. | P & C (1992 p. 226) | MH |
Establishment requirements? | Established in open areas e.g. Grazing land and neglected areas. | P & C (1992 p. 225) | ML |
How much disturbance is required? | “In Victoria it has become a weed of grazing land and neglected areas”. | P & C (1992 p. 225) | ML |
Growth/Competitive | |||
Life form? | Erect perennial herb. Other. | P & C (1992 p. 225) | L |
Allelopathic properties? | No Allelopathic properties described. | L | |
Tolerates herb pressure? | “The rosette leaves are rarely eaten by stock and the aerial growth is never grazed because of the stout spines on the rigid leaves”. | P & C (1992 p. 227) | H |
Normal growth rate? | Other more rapidly growing thistles e.g. Silybum marianum, Acanthospermum hispidum. | P & C (1992 p. 230) | ML |
Stress tolerance to frost, drought, w/logg, sal. etc? | Tolerant of drought (occurs in central Victoria). (No other information on stress tolerance in P & C 1992). | P & C (1992 p. 225) | M |
Reproduction | |||
Reproductive system | “Reproducing from a perennial taproot and by seed”. | P & C (1992 p. 225) | H |
Number of propagules produced? | “The viability of the seed is about 70%”. Not stated to be numerous or few. | P & C (1992 p. 226) | M |
Propagule longevity? | ? | M | |
Reproductive period? | “The large taproot stays alive and produces new aerial growth each autumn”. Therefore assumed to produce propagules for > 3 years. | P & C (1992 p. 226) | MH |
Time to reproductive maturity? | Seeds germinate autumn/winter/spring develop a rosette in summer without producing a flowering stem flowering stem produced in spring/early summer, flowers in late spring and summer. | P & C (1992 p. 226) | MH |
Dispersal | |||
Number of mechanisms? | See ‘dispersal’ section in P & C (1992 p. 226 & 227). | MH | |
How far do they disperse? | As above. | MH |
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