Diffuse knapweed (Noxious Weeds of Colorado)

Diffuse knapweed

Centaurea diffusa

Summary ⁴

Diffuse Knapweed (Centaurea diffusa), also known as White Knapweed or Tumble Knapweed, is a biennial forb native to Eurasia. During the first year of growth, it produces a rosette in spring or fall. During the second year the stem bolts, flowers, sets seed, and the plant dies. Once dried up, it breaks off at ground level and becomes a tumbleweed which disperses the seeds over long distances. A mature plant can produce up to 18,000 seeds per plant. Diffuse knapweed can grow 1 to 3 feet tall, and is diffusely branched above ground. Leaves are small, and are reduced in size near the flowering heads. Flowers are white or purple, urn-shaped, and located on each branch tip. Flowering occurs July-August. Bracts enclosing the flowerheads have 4 or 5 pairs of lateral spines and are tipped with a distinct slender terminal spine.

Source:
https://drive.google.com/file/d/1ryGRysI-vtgWGLVaX5Nx58-qao7FJ8QT/view
http://www.cwma.org/DiffuseKnapweed.html

Identification ⁵

Height: 1-3 feet tall
Shape: Upright forb
Flowers: Flowerheads are broadly urn-shaped, 0.6-0.8 in tall, solitary or in clusters of 2-3 at the ends of the branches. Bracts have 4-5 pairs of lateral spines and are tipped with a distinct slender terminal spine. The flowerhead has ray flowers surrounding tubular disk flowers. The ray flowers are white, rose-purple, to lavender. Flowers June-Aug.
Stems: One or more upright stems, highly branched, angled, with short, stiff hairs on the angles
Leaves: Basal leaves are stalked and divided into narrow, hairy segments in a rosette. Stem leaves are smaller, alternate, less divided, stalkless, and become bract-like near the flower clusters
Fruit: Seeds are light brown to black
Toxic: Sap may cause skin irritation in some people
Root: Has a stout taproot

Source:
https://drive.google.com/file/d/1ryGRysI-vtgWGLVaX5Nx58-qao7FJ8QT/view
http://www.cwma.org/DiffuseKnapweed.html

Origin/Habitat ⁵

Diffuse knapweed is native to Eurasia. Diffuse knapweed is found on disturbed or overgrazed areas such as rangelands, roadsides, trails, and forested benchlands. It is generally found on light, dry, porous soils and can tolerate arid conditions. It prefers open habitats rather than shaded areas. Diffuse knapweed is not common on cultivated lands or irrigated pasture because it cannot tolerate cultivation or excessive moisture. It contains allelopathic chemicals, which allows it to suppress competitive plant growth and create single species stands.

Source:
https://drive.google.com/file/d/1ryGRysI-vtgWGLVaX5Nx58-qao7FJ8QT/view
http://www.cwma.org/DiffuseKnapweed.html

Sources and Credits

(c) Franz Xaver, some rights reserved (CC BY-SA), https://upload.wikimedia.org/wikipedia/commons/4/47/Centaurea_diffusa_1.jpg
(c) CK Kelly, some rights reserved (CC BY), uploaded by CK Kelly
(c) Dr. Lindsie McCabe, some rights reserved (CC BY-NC), https://picasaweb.google.com/107142014359091466819/6450126030583195297#6450214398005061762
Adapted by Colorado Parks and Wildlife from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Centaurea_diffusa
(c) Colorado Parks and Wildlife, some rights reserved (CC BY-SA)

More Info

iNat Map

Color	pink, white
Species status	List B
Growth form	Flowering Plants

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