SafePlants

Diffuse Knapweed (Centaurea diffusa)

Diffuse Knapweed, scientifically known as Centaurea diffusa, is also commonly referred to as White Knapweed or Tumble Knapweed.

Considerations for Pets

• The text mentions sharp spines at the end of the bracts, which could pose a risk of injury.

Taxonomy and Nomenclature

• Scientific Name: Centaurea diffusa
• Common Names: White Knapweed, Tumble Knapweed, Spreading Knapweed
• Family: Asteraceae (Sunflower Family)
• Genus: Centaurea
• Synonyms: Centaurea diffusa Lam.

Distribution and Habitat

• Native to Eastern Europe and Western Asia, specifically Central Europe, east to central Russia, Caucasia, and western Siberia.
• Introduced to North America, including the northeast and north-central U.S., the Pacific Coast, Idaho, and Montana.
• Found in dry, light, porous soils.

Ecological Role

• Considered an invasive species in many regions, including North America and Montana.
• Class B Noxious Weed in King County.
• Listed as a Class B weed in some regions, with requirements for property owners to control its spread.
• Suppresses other vegetation, presumably through competition for soil water.
• Reduces productivity of grazing lands and wildlife habitat and increases surface runoff.

Morphological Characteristics

• Biennial, annual, or short-lived perennial plant.
• Grows to a height of 8-40 inches (20.3-101.6 cm), or up to two feet tall.
• Branched stems covered in short, dense hairs.
• Elongated, fibrous taproot.
• Basal leaves grow 7 to 8 inches long.
• Rosette leaves have finely divided lobes.
• Distinguished by sharp spines at the end of the bracts.

Reproduction and Life Cycle

• Reproduces entirely from abundant seeds that germinate quickly.
• Forms a long, fibrous taproot and a rosette.
• Seed remains viable in the soil for up to five years.
• Completes its lifecycle within two years as a biennial.
• Can live for several years as a rosette before flowering.

Interactions with Other Organisms

• Competition with associated grasses for resources.
• Subject to biocontrol efforts using insects that lay eggs on the root.

Quirky Facts

• Diffuse knapweed was likely introduced accidentally in alfalfa seed.

Further Information

• USDA's National Invasive Species Information Center.
• Weed Science (wsweedscience.org).
• California Invasive Species Council (cal-ipc.org).
• abinvasives.ca (Last Updated January 2014).