These weeds cover a lot of territory--look at the range below! (They are found many other places too, but the range we indicated is where they are really bad problems.)

The bane of the Californian central valley, yellow starthistle, and the various knapweeds of the US west are all siblings in the genus Centaurea. Gardeners can relax because bachelor's buttons (also in the genus Centaurea) are non-invasive. The knapweeds monopolize fields, reducing the land's biodiversity and forage value. Horses that feed upon yellow starthistle develop an incurable and fatal brain disease.



Learn more about yellow starthistle!
Learn more about Russian knapweed!
Learn more about spotted knapweed!
...or click on the map of the USA above to see another weed!