Diffuse knapweed is a prohibited invasive species. It is illegal to possess, import, purchase, transport, or introduce these species (including hybrids or cultivars) except under a permit or statutory exemption. Transport directly to the Minnesota Department of Natural Resources in a sealed container for identification or reporting purposes is permitted.
- Diffuse knapweed is found in well-drained soils, gravel pits, trails, pastures and roadsides.
- It can alter the soil chemistry, inhibiting the growth of surrounding plants.
- It outcompetes native vegetation, reducing diversity and resulting in soil erosion.
Diffuse knapweed should be reported. The Minnesota Department of Natural Resources provides detailed recommendations for reporting invasive species.
How to identify diffuse knapweed
- Diffuse knapweed (Centaurea diffusa) is a biennial or short-lived perennial that forms a basal rosette in its first year and bolts during second year growth.
- When mature, this knapweed tends to be shorter than other knapweeds, usually reaching one to three feet in height.
- Multiple rough-textured branching stems.
- Basal leaves are deeply divided into long and narrow lobes.
- As leaves move up the stem, they get smaller with fewer lobes, sometimes lacking lobes entirely.
- Leaves are covered with very fine hairs.
- Each flower head is a cluster of small flowers but appear as a single flower.
- White to pink/purple urn-shaped leaves with leathery bracts, each having a small spine at the tip.
- These flowers can be solitary or part of a cluster at the end of a branch.
- Flowers bloom July to August.
- Very small and dark brown in color.
- Diffuse knapweed reproduces solely by seed.
- One plant can produce up to 18,000 seeds.
- Plants have taproots.
Reviewed in 2019