Title: Onopordum acanthium L.

Scientific Name: Onopordum acanthium L.

Common Names: scotch thistle, heraldic thistle, cotton thistle



Source & more images (via ALA)

Habitat: Scotch thistle prefers subhumid temperate regions and grows well in soils of moderate to high fertility. The weed is competitive in annual rainfall areas of 500-850 mm. It does not grow well on waterlogged soils.

Distribution:



Original source via CABI


Invasiveness Assessment

ESTABLISHMENT


1. Germination requirements? “Seeds germinate at any time of year”.P & C (1992 p. 217)

2. Establishment requirements? Occur in open areas e.g. pastures.

3. How much disturbance is required? “Favours clover and Lucerne pastures and fertile river flats more than areas of unimproved native vegetation”.P & C (1992 p. 217)

GROWTH / COMPETITIVE


4. Life form? Annual or biennial herb. Other.P & C (1992 p. 216)

5. Allelopathic properties? No Allelopathic properties described.

6. Tolerates herb pressure? “The weed is rejected by stock because of the above spines”.P & C (1992 p. 218)

7. Normal growth rate? “It is a competitive weed of Australian pastures”. “In New South Wales, Scotch Thistle occurs with the closely related Illyrian thistle and some infestations in the State are a mixture of the two species plus various intermediate taxa”. (P & C 1992 pp.216, 218).

8. Stress tolerance to frost, drought, w/logg, sal. etc? Assumed tolerant of frost (occurs in S. Tas.) and drought (occurs in C. Vic. & NSW).P & C (1992 p. 216)

REPRODUCTION


9. Reproductive system? Reproducing by need”. P & C (1992 p. 216). “There can be some local spread of severed root pieces”. P & C (1992 p. 217)

10. Number of propagules produced? “A prolific seeder and a single plant may produce over 20,000 seeds”.P & C (1992 p. 218)

11. Propagule longevity? “Buries seed is long lived and germinates when brought near the surface hence, plants may appear on recently cultivates areas where there has been no seeding for several years”.P & C (1992 p. 218)

12. Reproductive period? Annual or biennial herb. P & C (1992 p. 216)

13. Time to reproductive maturity? Annual or biennial herb.P & C (1992 p. 216)

DISPERSAL


14. Number of mechanisms? Equipment, wool, clothing, wind, animals (internal) and possibly birds. P & C (1992 p. 217)

15. How far do they disperse? “Seeds remain viable after passing through the digestive tracks of sheep”.P & C (1992 p. 217)


Impact Assessment

RECREATION


1. Restrict human access? Erect annual or biennial herb commonly 1 to 1.2 metres. Comprises one main stem with numerous branches and broad spiny wings. Leaves also spiny. Dense patches would impede individual access, and the spiny nature of the plant would be highly annoying.P & C (2001)

2. Reduce tourism? Because of the spiny nature of the plant, dense patches occurring in recreational areas would restrict human activities.

3. Injurious to people? Spines can be present for most of the year. “Dead plants remain standing for many months.” P & C (2001)

4. Damage to cultural sites? Roots comprise of a stout taproot; unlikely to affect structures. Dense patches would create a moderate negative visual effect particularly with dead plants remaining, seriously affecting the aesthetics of an area.P & C (2001)

ABIOTIC


5. Impact flow? Terrestrial species.P & C (2001)

6. Impact water quality? Terrestrial species P & C (2001)

7. Increase soil erosion? “Seeds germinate at any time of year, hence infestations consist of plants of various ages and sizes.” Root system is a stout taproot. Not likely to affect soil erosion.P & C (2001)

8. Reduce biomass? “It occurs as a competitive weed of Australian pastures.” Plant replaces biomass.P & C (2001)

9. Change fire regime? “Dead plants remain standing for many months.” Dense infestations may create a minor change to the frequency of fire risk.P & C (2001)

COMMUNITY HABITAT


10(a) Impact on composition of high value EVC? EVC=Grassy woodland (E); CMA=Port Phillip; Bioreg=Central Victorian Uplands; VH CLIMATE potential.
Grows best on moderate to high fertility soils rather than unimproved native vegetation. Competes with pasture species. Likely to have a minor impact on grasses/forbs in natural ecosystems. Impact also limited by overstorey cover.P & C (2001

10(b) Impact on medium value EVC? EVC=Riverine grassy woodland (E); CMA=Goulburn Broken; Bioreg=Murray Fans; VH CLIMATE potential.
Impact as in 10(a) above. P & C (2001)

10(c) Impact on low value EVC? Does not appear likely to occur in any low value EVC in Victoria.

11. Impact on structure? “…its relatively large leaves smother other plants. As it survives well into summer, there is little chance of the other species recovering.” However, it grows best on moderate to high fertility soils rather than unimproved native vegetation. Likely to have a minor effect on the floral strata.P & C (2001)

12. Effect on threatened flora? Non recorded.

FAUNA


13. Effect on threatened fauna? Non recorded.


14. Effect on non-threatened fauna? “The weed is rejected by stock because of the dense spines.” Competitive nature and physical properties would reduce food source for native animals.P & C (2001)

15. Benefits fauna? No known benefits to fauna.

16. Injurious to fauna? “If it is eaten, the spines cause mechanical damage, particularly around the mouths and eyes of animals.” Spines present for much of the year.P & C (2001)

PEST ANIMAL


17. Food source to pests? Birds are known to eat the seed. Potential food source to pest birds.P & C (2001)

18. Provides harbor? Not known to provide harbor.

AGRICULTURE


19. Impact yield? “Newly sown pastures are often overrun by a high germination of thistle seeds and, later, its relatively large leaves smother other plants. As it survives well into summer, there is little chance of the other species recovering.” Serious impact on forage production leading to reduced carrying capacity.P & C (2001)

20. Impact quality? “…contributes to vegetable fault in wool.” Major impact on quality of produce.P & C (2001)

21. Affect land values? No evidence of effect on land value. Reduction in forage production due to presence of the weed may reduce values slightly.

22. Change land use? Goats are known to graze the flowering plants in summer and autumn. To control the plant while retaining some agricultural return, a change in land use may be dictated

23. Increase harvest costs? Not known to affect harvest costs.

24. Disease host/vector? None evident.




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Do you have additional information about this plant that will improve the quality of the assessment? If so, we would value your contribution.


Assessment ratings originally made by the Victorian Department of Primary Industries.
The entry of this assessment was made possible through the generous support of the Weed Society of New South Wales.






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Date: 13 December 2011; 1:59:06 PM AEDT

Author Name: David Low
Author ID: adminDavid