Invasive species:


Bighead Knapweed


Bighead Knapweed, or Centaurea macrocephala, is also known as armenian basketflower, globe centau- rea, golden thistle, yellow or lemon fluff knapweed and yellow hardhead.


Overview: Bighead knapweed is


a long-lived


perennial herb native to the Cauca- sus region of Eastern Europe. It has been a cultivated ornamental for over 200 years. Introduced to the UK and North America in the early 1800s, it is still widely available in the horticul- tural trade as seed, plants, and cut/dried flowers. This knapweed reproduces by seed but may be propagated by divid- ing the crown. Its tap root develops a woody crown with age. This is the larg- est Centaurea in cultivation or natural- ized, so is easily identified. Bighead knapweed flowers July to


September. Mature seed heads open to disperse the seed. Although seeds are plumed, they are too heavy to be wind dispersed but can attach to animal hair/ fur. Bighead knapweed needs distur-


bance to establish but is then difficult to control. Eradication efforts of a four hectare infestation in Washington state have been ongoing for about 25 years. It competes with native vegetation for nutrients and light.


Introduced to North America in the early 1800s, Knapweed has become so well established it is now considered to be an invasive species.


6 • Early Spring 2015 localgardener.net


Photo by Meneerke Bloem.


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