Centaurea nigra L.

Title: Centaurea nigra L.

Scientific Name:

Centaurea nigra L.

Common Names:

black knapweed, common knapweed, lesser knapweed

Image source

Habitat: Subhumid and cool temperate regions. In Victoria it is confined to a few locations occurring on roadsides and in pastures on fertile soils where annual rainfall is more than 750 mm. Cultivation can spread black knapweed.

Distribution:

Original source via GBIF

Invasiveness Assessment

ESTABLISHMENT

1. Germination requirements? "Seeds germinate in autumn and spring and new growth is produced from root buds about September." Requires normal seasonal changes (spring temperatures and rainfall) (Parsons and Cuthbertson, 2001)

2. Establishment requirements? Confined to roadsides and pastures on fertile soils where annual rainfall is more than 750 mm. In Washington state in the U.S. it, "... appears to have become part of the meadow knapweed complex." May establish under moderate litter cover (NWCB; Parsons and Cuthbertson, 2001).

3. How much disturbance is required? See comment above. It may occur in relatively intact grasslands or open situations (NWCB; Parsons and Cuthbertson, 2001).

GROWTH / COMPETITIVE

4. Life form? Perennial herb reproducing from root buds. Geophyte. (Parsons and Cuthbertson, 2001)

5. Allelopathic properties? "There is overseas evidence that plants produce allelopathic compounds reducing germination and early seedling development of some other species." (Parsons and Cuthbertson, 2001).

6. Tolerates herb pressure? "Black knapweed is not eaten by grazing animals and its presence in pastures reduces carrying capacity." Favoured by heavy grazing pressure as the plant is not eaten(Parsons and Cuthbertson, 2001).

7. Normal growth rate? No information on the growth rate of this species is available. It is known as an aggressive and invasive species in pastures and meadows in the U.S. Growth rate may be equal to species of same life form (NWCB).

8. Stress tolerance to frost, drought, w/logg, sal. etc? No recorded information available. Plant favour sub-humid, cool-temperate environments where annual rainfall is more than 750 mm. Aerial growth dies back in autumn, but plant remain as dormant roots over winter. Withstand frost, but may not tolerate drought. Immunity to other stresses not known (Parsons and Cuthbertson, 2001).

REPRODUCTION

9. Reproductive system? Reproduces sexually and vegetatively (Parsons and Cuthbertson, 2001).

10. Number of propagules produced? "Black knapweed... can produce more than 1000 seeds/plant." (DAFF)

11. Propagule longevity? No data available. A related species Centaurea debauxii, believed to be a hybrid of C. nigra and C. jacea, is know to produce seeds that, "...remain viable in the soil for several years." C. nigra may demonstrate similar seed longevity (DAFF).

12. Reproductive period? A perennial plant with creeping horizontal and vertical roots. Mature plant may produce propagules for more than two years. (Parsons and Cuthbertson, 2001).

13. Time to reproductive maturity? "Aerial growth develops during spring and plants flower from November to February before dying back in autumn." Reaches maturity to produce viable propagules in under one year. (Parsons and Cuthbertson, 2001).

DISPERSAL

14. Number of mechanisms? "The seed is not equipped with an effective pappus and so wind dispersal is not important; however, seeds can become attached to wool, hides machinery, bags etc." Propagules spread by attaching to animals or humans. (Parsons and Cuthbertson, 2001).

15. How far do they disperse? Migratory birds have been implicated in long distance dispersal. "Seeds fall near the parent plant but can be transported by water or birds. Seeds remain viable in the stomachs of migrating Kildeer for up to 144 hours, and can pass through animals with little or no damage. Quail may retain the seed for 24 hours, ducks 5, and geese 19, lesser yellowlegs 6 hours. (Parsons and Cuthbertson, 2001).

Impact Assessment

RECREATION

1. Restrict human access? An erect perennial herb to 20 to 90 cm high. A common plant of meadows in its native range, it has little impact on human access (Parsons and Cuthbertson, 2001).

2. Reduce tourism? The plant is not likely to affect recreational activities. Its presence may a have a minor effect on the aesthetics of an area.

3. Injurious to people? It does not have any spines or burrs, nor is the plant toxic. The roots and seeds have been used ancient European medicines. (Parsons and Cuthbertson, 2001).

4. Damage to cultural sites? C. nigra has been shown to be aggressive and invasive in pastures and meadows. Its presence would create a moderate visual impact (WSNWCB).

ABIOTIC

5. Impact flow? Terrestrial species (Parsons and Cuthbertson, 2001).

6. Impact water quality? Terrestrial species (Parsons and Cuthbertson, 2001).

7. Increase soil erosion? The plant is aggressive and competes well against grasses, and the aerial parts of the plant die off in autumn. It has the potential to leave areas of bare soil, possibly resulting in erosion (WSNWCB; Fisher et al., 1996)

8. Reduce biomass? Replaces grass species. Little or no change in biomass. (Fisher et al., 1996).

9. Change fire regime? Competes well against grasses. Similar fire potential as displaced vegetation. Little change to frequency of fire risk.

COMMUNITY HABITAT

10(a) Impact on composition of high value EVC? EVC=Plains grassland (E); CMA=Glenelg Hopkins; Bioreg=Victorian Volcanic Plain; VH CLIMATE potential. It is an aggressive and invasive species in pastures and meadows in the U.S. Potential to seriously affect grasses and ground covers (WSNWCB)>

10(b) Impact on medium value EVC? EVC=Grassy dry forest (D); CMA=Glenelg Hopkins; Bioreg=Victorian Volcanic Plain; VH CLIMATE potential. Similar impact as in 10(a) above. More commonly occurs in open areas (roadsides, pasture, waste places). Therefore, population density may be restricted by overstorey cover (Moore & Frankton, 1974).

10(c) Impact on low value EVC? EVC=Lowland forest (D); CMA=Glenelg Hopkins; Bioreg=Victorian Volcanic Plain; VH CLIMATE potential. Similar impact as in 10(b) above (Moore & Frankton, 1974).

11. Impact on structure? "It invades overgrazed or underdeveloped pastures, and there is evidence that the plants produce allelopathic compounds reducing germination and early seedling development of some other species. It may have a major negative impact on the lower stratum. In the U.S., it is aggressive and invasive in pastures and meadows (Parsons and Cuthbertson, 2001; WSNWCB).

12. Effect on threatened flora?

FAUNA

13. Effect on threatened fauna?

14. Effect on non-threatened fauna? Not known as a serious weed of natural ecosystems in Victoria (it is not recorded in Carr et al (1992)). Its presence in pastures reduces carrying capacity. Assume its presence would also reduce available food for non-threatened fauna (Parsons and Cuthbertson, 2001).

15. Benefits fauna? No known benefits.

16. Injurious to fauna? No known toxic principles.

PEST ANIMAL

17. Food source to pests? Not known as a food source for pest animals.

18. Provides harbor? A perennial herb with erect stems and narrow leaves; the aerial parts die back leaving little vegetative cover. Unlikely to provide harbor (Parsons and Cuthbertson, 2001)

AGRICULTURE

19. Impact yield? Its presence in pasture reduces the carrying capacity. Considered to be allelopathic. Competes well against grasses. Considered a serious crop weed, but impact in cropping situations not known. In the U.S., it is known as aggressive, invasive species, particularly in pastures and meadows (Fisher et al., 1996; Parsons and Cuthbertson, 2001).

20. Impact quality? "No known impact on quality of harvest/produce.

21. Affect land values? The plant seriously affects yield and it requires a concerted control program for several years to eradicate it. This would have a negative influence on price, depending upon type of agricultural activity (Parsons and Cuthbertson, 2001).

22. Change land use? "The recommended method of control is to use herbicides; cultivation is not effective. Land used for grazing purposes may be restricted while control activities undertaken. Temporary loss of land use (Parsons and Cuthbertson, 2001).

23. Increase harvest costs? No evidence of increasing harvest costs.

24. Disease host/vector? None evident.

Feedback

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's Network.

Attachments:

nigra via kew.JPG
Capture.JPG

referenced by (4)

wra1008: Common Names - L (via lesser knapweed)wra997: Common Name - C (via common knapweed)wra881: Invasive Plants - Common Name - B (via black knapweed)wra825: Common Name - B (via black knapweed)

Article: wra612 (permalink)
Categories: :wra:c, :wra:inv1, :wra:invmh, :wra:inv2, :wra:inv3, :wra:inv4, :wra:invml, :wra:inv5, :wra:inv6, :wra:invh, :wra:inv7, :wra:invm, :wra:inv8, :wra:inv9, :wra:inv10, :wra:inv11, :wra:inv12, :wra:inv13, :wra:inv14, :wra:inv15, :wra:imp1, :wra:impl, :wra:imp2, :wra:impml, :wra:imp3, :wra:imp4, :wra:imp5, :wra:imp6, :wra:imp7, :wra:imp8, :wra:imp9, :wra:imp10a, :wra:impmh, :wra:imp10b, :wra:imp10c, :wra:imp11, :wra:imp12, :wra:impm, :wra:imp13, :wra:imp14, :wra:imp15, :wra:imph, :wra:imp16, :wra:imp17, :wra:imp18, :wra:imp19, :wra:imp20, :wra:imp21, :wra:imp22, :wra:imp23, :wra:imp24
Date: 31 July 2009; 11:03:58 AM AEST

Author Name: David Low
Author ID: adminDavid