Invasiveness Assessment - Taurian thistle (Onopordum tauricum) 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. |
The following table provides information on the invasiveness of Taurian 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: Taurian thistle
Scientific name: Onopordum tauricum
| Question | Comments | Confidence | Rating |
| Establishment | |||
| Germination requirements? | “Plants typically germinate in fall [autumn] after first rains” (Healy, Enloe & DiTomaso, 2005). | MH | MH |
| Establishment requirements? | “Seedlings do not compete well with established perennial grasses” (Healy, Enloe & DiTomaso, 2005). Requires open space to establish. | ML | MH |
| How much disturbance is required? | Invades pasture, roadsides and waste places (Groves et. al, 2002), steppe, open scrub and fallow fields (Davis, 1975), drainage creeks (MCA, 2006). Establishes in highly disturbed ecosystems. | ML | H |
| Growth/Competitive | |||
| Life form? | “Tall biennial thistle” (Groves, et. al, 2002) up to 2 m (Tutin, 1980). | L | MH |
| Allelopathic properties? | None found, but there is little information about the biology of this species. | M | L |
| Tolerates herb pressure? | Leaves and stems bear spines up to 1.5 cm long (Davis, 1975), which seems to deter most vertebrates, except perhaps for goats who eat the seed heads of the related O. illyricum (Holst & Allan, 1996). Weevils were introduced to Australia to control this genus in 1992, but it was found that less than 20% of O. tauricum capitula were attacked (Briese, 2000). Taurian thistles are still capable of seed production under most herbivory pressure. | MH | MH |
| Normal growth rate? | Vigorous (Healy, Enloe & DiTomaso, 2005). | H | MH |
| Stress tolerance to frost, drought, w/logg, sal. etc? | “Mature plants have been found [in Monterey, California] in very dry years” (MCA, 2006). Seed germination stimulated by fire (Healy, Enloe & DiTomaso, 2005), but no record of fire tolerance, nor tolerances to frost, salinity or waterlogging. | M | L |
| Reproduction | |||
| Reproductive system | “Reproduce solely by seed” (Briese, 2000). No pollination information found. | M | L |
| Number of propagules produced? | Capitulum “produce up to several hundred seeds each,” (Briese, 2000), which, when multiplied by the 43 seed and flower heads pictured in Healy, Enloe & DiTomaso (2005), comes to 4 300 seeds. | H | MH |
| Propagule longevity? | “Buried seed [of Onopordum spp.] may persist for up to twenty years” (Healy, Enloe & DiTomaso, 2005). “Taurian thistle seeds are capable of long dormancy” (MCA, 2006) | H | MH |
| Reproductive period? | “Flowering stems develop during the second spring/summer season” (Healy, Enloe & DiTomaso, 2005) on this biennial plant (Groves, et. al, 2002), so that they produce seed for only one year. | L | MH |
| Time to reproductive maturity? | “Flowering stems develop during the second spring/summer season” (Healy, Enloe & DiTomaso, 2005), within two years of germination | MH | MH |
| Dispersal | |||
| Number of mechanisms? | Propagules dispersed externally by animals, adapted to wind dispersal and buoyant (Cunningham et al, 2003) | MH | MH |
| How far do they disperse? | Very few to none will disperse to 1 km (via drainage creeks (MCA, 2006)), most 20-200 m (via wind and animals, see Q 14). | ML | MH |
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