Centaurea stoebe ssp. micranthos - Banner
Image Information
Location: Taney County, Missouri
Month of Photograph: July
Distribution Map: Centaurea stoebe ssp. micranthos -Distribution Map Spacer
USDA, NRCS. 2012. The PLANTS Database (http://plants.usda.gov, 16 January 2012). National Plant Data Team, Greensboro, NC 27401-4901 USA. Spacer Guests can be assured that there is established evidence that this plant has been found in all of the green filled counties of Arkansas. However, the white filled counties should not be interpreted as counties in which this plant does not grow. They should instead be interpreted as counties which lack officially sanction evidence of the plants presence there.

Family: Asteracea

Flower, lateral View

Centaurea biebersteinii - Flower Lateral View "
Not all images on this page were photographed on the same day or at the same location. The precise location and date that specific photographs were taken can be obtained by email.
Centaurea biebersteinii - Ipper Plant Upper Plant

 

Centaurea biebersteinii - Stem and LeavesStem and Leaf
Centaurea biebersteinii - Leaf adaxialLeaf, adaxial
Centaurea biebersteinii - Lobe of LeafLobe of Leaf
Centaurea biebersteinii - Flower Bud Flower Bud
Centaurea biebersteinii - Leaf Close Up Leaf, close up
Centaurea biebersteinii - Stem Stem
Flower, close up
Centaurea biebersteinii - Flower Close Up

Ribbed Pubescent Stem and Leaf, close up
Centaurea biebersteinii - Stem Close Up

Physical Description, Encyclopedia of Life, by Dr. John Hilty

This adventive plant is a short-lived perennial about 2-3' tall. It branches occasionally to frequently, becoming broader toward the flowering stems. The stems are ribbed and pubescent with a stiff woody texture. The alternate leaves are up to 3½" long and 1½" across; they are sparsely distributed along the stems. They are pubescent and pinnately lobed; these lobes are narrow, and the terminal lobe of each leaf is usually the longest. If the basal leaves haven't withered away, they are somewhat larger than the cauline leaves and deeply pinnatifid. Both the stems and the foliage are whitish or greyish green, although the base of the central stem often turns brown with age. The upper stems terminate in flowerheads about ¾" across. Each flowerhead consists of numerous ray florets that are pink to purplish pink, overlapping floral bracts that are greyish green, and no disk florets. Each floral bract is ovate, tapering to a black tip with coarse short bristles that are dull white to brownish black; there are several dark green veins toward the base of each bract.

These bracts are appressed together. The ray florets are slender, thread-like, and branching; the outer florets are the longest and sterile. The blooming period occurs from mid-summer to early fall and lasts about 1-2 months. Each floret is replaced by an oblong achene that has a crown of short bristles on top; these bristles may fall off. The root system consists of a taproot. It often forms colonies at favorable sites, and spreads by reseeding itself. The achenes are spread to a limited extent by the wind.

Hilty, John, Dr. "Centaurea Stoebe Subsp. Australis — Details." Encyclopedia of Life. EOL Executive Committee, n.d. Web. 31 July 2013.

For more information see the detailed paper by the "Alien Plant Working Group" of the "Plant Conservation Alliances" titled "Fact Sheet: Spotted Knapweed".

Physical Description, Encyclopedia of Life, supplier U.S National Park Service

Spotted knapweed was accidentally introduced into North America in the late 1800s in contaminated alfalfa and clover seed and in soil used for ship ballast. In North America, plants generally live 3 to 7 years but can live up to nine years or longer and regrow from buds on the root crown. Reproduction is by seed. Individual plants are capable of producing an estimated 500-4,000 seeds per square foot per year. Most of the seed is viable at the time of dispersal and can remain viable in the soil for 5-8 years. Most seed is dispersed near the parent plant but can be moved great distances by people, livestock, wildlife, and vehicles and in soil, crop seed, and contaminated hay.

Swearingen, J., B. Slattery, K. Reshetiloff, and S. Zwicker. 2010. Plant Invaders of Mid-Atlantic Natural Areas, 4th ed. National Park Service and U.S. Fish and Wildlife Service. Washington, DC. 168pp.