[Knapweeds of the Columbia River Gorge of Oregon and Washington]

Diffuse Knapweed, Tumble Knapweed, White Knapweed

Centaurea diffusa

Diffuse Knapweed, Tumble Knapweed, White Knapweed: Centaurea diffusa

The photo above shows the flower head of tumble knapweed as seen at about 3000' on the south side of Mt. Adams...................August 25, 2005. Note the long spine at the tip of each light involucral bract, and the numerous comb-like lateral spines.

Diffuse Knapweed, Tumble Knapweed, White Knapweed: Centaurea diffusaThe photo at right shows the branching form of Centaurea diffusa from the airport at the Dallesport, WA.............June 26, 1991. Note the open branching of the stiff stems.
Characteristics:

Tumble knapweed is an erect, widely branched annual or biennial from 10-60 cm tall. The pinnatifid leaves are small. The leaves are reduced in size upwards on the stem, becoming entire in the inflorescence.

The numerous flower heads are narrow, with the involucre 8-10 mm tall, and the middle and outer bracts coarsely comb-like or spiny. The spines range from 1.5-4 mm long. Individual flower heads are few flowered, with the flowers white to occasionally purple.

 


Habitat:

Tumble knapweed may be found in disturbed places such as fields, waste places, and roadsides.


Range:

Native to the Mediterranean region, tumble knapweed is found over much of the United States.

In the Columbia River Gorge, it is primarily found between the west and east ends of the gorge between the elevations of 100'-3000'.


Basal leaves of Diffuse Knapweed, Tumble Knapweed, White Knapweed: Centaurea diffusa

Basal leaves of tumble knapweed as seen on Mill Creek Ridge (Columbia Land Trust Property) outside The Dalles, Oregon...........December 5, 2013.

Stem leaf of Diffuse Knapweed, Tumble Knapweed, White Knapweed: Centaurea diffusa

A stem leaf of tumble knapweed.

Paul Slichter