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Spotted Knapweed

Centaurea stoebe L.

(synonyms:  Centaurea biebersteinii and Centaurea maculosa)

Asteraceae (Sunflower Family)

▲▼ seedlings

▲▼ rosettes of young plants

▲▼ rosettes of young plants

▲▼ rosettes of young plants

▲▼ first year rosette of compact, deeply lobed leaves

▲▼ young plants initiating flowering stems

▲ leaves on stem that will produce flowers

▲ ▼ mature plants with stiff, gray stems, deeply divided gray-green leaves and pinkish-lavender flower heads

▲ flowering (top) and non-flowering (lower front) portions of a spotted knapweed plant

▲ Close up of flowering stems

▲ ▼ flowers

▲▼ inflorescence/flowers

▲ flower bud showing characteristic black tips of floral bracts

▲ new shoots from a plant that flowered previous year (example of a perennial spotted knapweed)

 

Centaurea stoebe L. Spotted Knapweed: (Bayer Code:  CENMA; US Code CEST8)

·         Biennial weed with grey-green, divided lower leaves, linear upper leaves; basal rosette has deeply divided leaves

·         Leaves very hairy  with grayish appearance; bracts under inflorescence have dark spots at tips

·         Grows 1-4' tall, forming much branched inflorescence structures

·         Head flowers are rose-pink, with 30-40 disk flowers per head, about 1 inch diameter, in June-August

·         Bracts below inflorescence have purplish-black tip, and are edged with tiny, short, dark spines

·         Found on roadsides, pastures, cultivated areas, non-crop areas; needs more moisture than other invasive knapweeds

·         Fairly rapidly increasing populations of spotted knapweed in southwest Missouri

·         Similar species not yet in Missouri:

     o   Diffuse knapweed (Centaurea diffusa) has similar basal leaves, but has white flowers and the bracts below the flower head are tan and edged with long, comb-like laterally-spreading spines

     o   Squarrose knapweed (Centaurea virgata) has somewhat similar leaves to spotted knapweed, but it has tan, comb-like bracts below the head, with bract tips that point away from the head

     o   Russian knapweed (Acroptilon repens) has more lanceolate leaves with shallow lobing, and papery bracts below the pink-flowered head inflorescence; Russian knapweed is also a creeping perennial, with deep, creeping roots

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Updated 23 January 2019