Invasiveness Assessment - Lacy ragweed (Ambrosia tenuifolia) 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.
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: Lacy ragweed
Scientific name: Ambrosia tenuifolia
| Question | Comments | Rating | Confidence |
| Establishment | |||
| Germination requirements? | Seeds germinate in autumn (Parsons & Cuthbertson 2001). Requires seasonal temperatures. | MH | MH |
| Establishment requirements? | Found principally in open areas (Parsons & Cuthbertson 2001). Limited establishment in shade. | ML | MH |
| How much disturbance is required? | Primarily a plant of disturbed open areas… ‘occurs as weed of roadsides, railway reserves, sand dunes, cultivated fields, stubble paddocks , degraded pastures, and waste places ’ (Parsons & Cuthbertson 2001). Establishes in highly disturbed natural ecosystems. | ML | MH |
| Growth/Competitive | |||
| Life form? | Perennial herbaceous plants (Parsons & Cuthbertson 2001). Life form – other. | L | MH |
| Allelopathic properties? | A. tenuifolia not documented to have Allelopathic properties (Parsons & Cuthbertson 2001). | L | MH |
| Tolerates herb pressure? | Not documented to be eaten by animals or insects (Parsons & Cuthbertson 2001). | H | MH |
| Normal growth rate? | Growth rate of A. tenuifolia is not documented. Others species have different growth rates. Therefore score as medium. | M | L |
| Stress tolerance to frost, drought, w/logg, sal. etc? | Susceptible to fire and waterlogging. Drought tolerant. Due to the locations it can be found, it appears to have saline tolerance. No documented evidence of ability to withstand frost (Parsons & Cuthbertson 2001). | MH | MH |
| Reproduction | |||
| Reproductive system | Reproduces sexually and vegetatively (Parsons & Cuthbertson 2001). | H | MH |
| Number of propagules produced? | “All types (of ragweed) are prolific seeders … average about 3000 seeds per year’ (Parsons & Cuthbertson 2001). | H | MH |
| Propagule longevity? | Annual ragweed propagule longevity is up to 40 years (Schmoll, Reigner & Harrison 2004). In contrast, giant ragweed is only viable for 6 weeks (Parsons & Cuthbertson 2001). No specific information on A. tenuifolia. Due to variation within genus, scored as medium. | M | H |
| Reproductive period? | Other ragweed species known to live up to 10 years. Lacy ragweed can form dense colonies (Parsons & Cuthbertson 2001). | H | MH |
| Time to reproductive maturity? | These three ragweed species reach maturity in approximately 9 months (Parsons & Cuthbertson 2001). | H | MH |
| Dispersal | |||
| Number of mechanisms? | Known to be dispersed by clinging to sheep, furred animals, bags, clothing, water, contaminated gravel and soil (Parsons & Cuthbertson 2001). | MH | MH |
| How far do they disperse? | Spreads ‘readily over long distances’. Hull provides buoyancy (Parsons & Cuthbertson 2001). Assume likely that some of the propagules will disperse greater than 1 km. | H | MH |
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