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spotted knapweed (Centaurea stoebe spp. micranthos)

 

COMMON NAMES:

spotted knapweed

 

SCIENTIFIC SYNONYMS:

Acosta maculosa auct. non (Lam.) Holub

Centaurea biebersteinii DC.

Centaurea maculosa auct. non Lam.

 

CONFIRMATION STATUS: Pending confirmation.

 

TAXONOMY: In its native range of Western, Central, and Eastern Europe, two sub-species have been identifie: Centaurea stoebe spp. stoebe is diploid and biennial, and subspecies Centaurea stoebe spp. micranthos is tetraploid and perennial.  The perennial subspecies is considered more invasive in Europe than the biennial subspecies.  The invasiveness of the North American taxon, Centaurea stoebe spp. micranthos, has been ascribed to it being perennial because it can tolerate dense vegetation once it has become established, whereas the biennial is more dependent on disturbance.

 

NATIVE STATUS: Introduced, United and Canada.

 

GENERAL BOTANICAL CHARACTERISTICS: 

 

Habit: Biennial or short-lived perennial herbaceous plant, 2 - 3' high and branch on the upper half.

 

Leaves: A basal rosette of leaves is produced the first year. Rosette leaves are deeply lobed, petiolate, and approximately 8 in. (20 cm) long and 2 in. wide. Stem leaves are alternate, grayish, hoary, and may be slightly lobed or linear. Leaves become smaller and less lobed toward the apex.

 

Flowers: Flowering plants are distinguished by the production of an upright (except when heavily grazed or repeatedly mowed) paniculate inflorescence with few to many branches. Flower heads develop on branch ends, are solitary or in clusters of two or three on the branch ends, ovate to oblong, ¼-inch wide and ½-inch long. Flower heads (which have been described as resembling pineapples) are distinguished by the comb-like fringed, black-tipped involucre bracts (giving the spotted look for which the plant is named) and the pink to light-purple flowers. 

Each flower head can have as many as 30 flowers each pro-ducing one seed. 

 

Fruits/Seeds: Mature oval seeds are brown to shiny black, 1/8 " - 1/4" long, with pale longitudinal lines, and a pappus of short, simple, and persistent bristles, and produced in erect, slender green pods which turn pale brown when mature.

 

Roots: Spotted knapweed has a stout taproot while lateral shoots form new rosettes near the parent plant.

 

REGENERATION PROCESS: Spotted knapweed reproduces only by seeds (although some vegetative expansion occurs with lateral shoots) and are distributed by the wind. Seed distribution also occurs dispersion by rodents, livestock and commercial hay.

 

HABITAT TYPES: In its native range spotted knapweed commonly grows in the forest-grassland interface on deep, well developed to dry soils.  It forms dense stands in more moist areas on well-drained soils including gravel, and on drier sites where summer precipitation is supplemented by runoff. In North America, spotted knapweed invades a wide variety of habitats including pastures, open forests, prairies, meadows, old fields, and disturbed areas. It displaces native vegetation and reduces the forage potential for wildlife and livestock. It is native to Europe and western Asia. It was accidentally introduced into North America in contaminated alfalfa and clover seed in the late 1800s.

 

SITE CHARACTERISTICS: Spotted knapweed invades open habitats, preferring full sun and can tolerate nutrient poor soils and harsh dry conditions.

 

SEASONAL DEVELOPMENT:  Plants bloom from Summer to early Fall (June to October).

 

GENERAL DISTRIBUTION: 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. Spottd knapweed is found throughout the United States (with possible exceptions of Texas, Oklahoma, and Mississippi) and throughout most of Canada (excepting Newfoundland, Manitoba, Saskatchewan, and northern regions of Nunavut).

 

SKY MEADOWS DISTRIBUTION: To be determined.

 

IMPORTANCE AND USES: Bee keepers value the flowers of spotted knapweed because of the flavorful honey produced from its nectar.

 

This plant is weedy or invasive in some regions or habitats and may displace desirable vegetation if not properly managed. Spotted knapweed is listed as noxious, prohibited, banned or otherwise regulated in 16 states.

 

 

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