Black Knapweed
Centaurea nigra L.
Family: Asteraceae
Description and life cycle
Black knapweed is a perennial with branching stems
growing 20 – 80 cm tall. Plants reproduce from a woody root
crown and lateral roots. Prostrate growing stems may develop
roots at their nodes when they come in contact with moist
soils. Broad basal leaves have stalks and shallow lobes.
Stem leaves are clasping and progressively become smaller
towards the top of the plant. Rose to lavender coloured
flowers appear from July to October. The round, broad blooms
are produced individually at stem tips and measure 1.3 cm
tall by 1 cm wide. Overlapping, fringed, comb-like bracts
are dark brown or black and bare a likeness to ‘ticks’.
About 60 ivory, linear-striped seeds, 4 mm long with short
pappus are produced in each head.
Biological control agent
References
Pacific Northwest Extension Publication. No Date. Idenfication of knapweeds and starthistles in the Pacific Northwest. Washington State Univer., Oregon State Univ., Univer. Idaho and U. S. Dept. Agric. PNW432. 23 p.
Wilson, Linda M. and Carol Bell Randall. Biology and biological control of knapweed.
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