Centaurea stoebe (Spotted Knapweed)

Plant Info
Also known as:
Genus:Centaurea
Family:Asteraceae (Aster)
Life cycle:biennial, short-lived perennial
Origin:Europe
Status:
  • Invasive - ERADICATE!
  • Noxious Weed
  • Prohibited or Restricted species
Habitat:sun; dry fields, roadsides, waste areas
Bloom season:June - October
Plant height:2 to 3 feet
Wetland Indicator Status:none
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: 7+petals Flower shape: tubular Cluster type: panicle Cluster type: round

[photo of flowers] Thistle-like flower heads 1 inch across, single at the ends of numerous branching stems. Each head consists of set of ray flowers around the outer edge and numerous, shorter disk flowers in the center. Ray flowers are sterile, widely spreading, narrowly tubular with 5 slender lobes as long as or longer than the tube. Disk flowers are fertile, erect to ascending, with a column of white-tipped stamens and a divided style. Flower color ranges from pink to purple, occasionally white, with the center disk flowers sometimes much paler than the outer flowers.

[photo of phyllaries] The bracts (phyllaries) surrounding the base of the flower are in several layers, usually appressed, green to purplish-brown, with obvious parallel veins and a dark brown to blackish appendage at the tip that is fringed in long, comb-like teeth, the teeth white to blackish-brown. The phyllary body is often wider than the appendage. The entire set of phyllaries (involucre) is 3/8 to ½ inch long and usually longer than wide. A mature plant has 25 to 100 flower heads.

Leaves and stem: Leaf attachment: alternate Leaf type: lobed Leaf type: simple

[photo of mid stem leaves] Leaves are basal and alternate, gray-green to blue-green, somewhat hairy, deeply lobed into narrow segments. Near the base of the plant leaves may be up to 8 inches long and 2 inches wide, becoming progressively smaller as they ascend the stem. Leaves near the flowers are typically small, more linear, and unlobed. Stems are stiff, ridged and roughly hairy, multiple from the base, and heavily branched. First-year plants produce only a basal rosette of leaves, with flowering stems emerging the second year.

Fruit: Fruit type: seed with plume

[photo of seed heads] Flower heads become seed heads about ½ inch long.

[photo of seeds] Seeds are elliptic, brown, finely hairy, 3 to 3.5 mm long with a tuft of short, light brown to white hairs at the tip.

Notes:

I hate this plant—it is taking over everywhere at my favorite local park. The flowers of Spotted Knapweed have been mistaken for Wild Bergamot (Monarda fistulosa), which it vaguely resembles, but the leaves and overall plant structure are very different between the two species. The stems and bracts are stiff and scratchy, making walking through a patch of this an uncomfortable experience. Spotted Knapweed is on the prohibited/control weed list for Minnesota and should be eradicated. It contains chemicals that poison the soil and inhibit native plants. The hundreds of seeds produced by one plant mostly stay within a few feet of the parent plant, thus it tends to form large, monoculture colonies. The first year it sprouts there is just a rosette of leaves, with flowers appearing the second year. Spotted Knapweed is one of 3 targeted plant species in Minnesota with an active bio-control program, the other 2 species are leafy spurge and purple loosestrife. Spotted Knapweed was formerly (or incorrectly) known as Centaurea biebersteinii and Centaurea maculosa. There are at least 2 recognized subspecies of C. stoebe, though they are poorly documented; subsp. micranthos is the species in North America.

The flower heads are very similar to other non-native, pink to purple flowered Centaurea species known to be in (or coming soon to) Minnesota, but the phyllaries of each species should be distinctive. Perhaps the most similar is Alpine Knapweed (Centaurea nigrescens); its phyllary body is not usually noticeably wider than the appendage, is narrowed just below the appendage so the appendage is more distinct from the body, and the teeth are more slender and always dark brown to black, never pale. Spotted Knapweed has the added distinction of leaves deeply lobed into narrow segments, where the other Knapweeds are either unlobed or less finely lobed.

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More photos

Photos by K. Chayka taken in Ramsey County. Photos by Peter M. Dziuk taken in Anoka, Kanabec and Pine counties.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Jess - Duluth
on: 2009-06-22 17:47:30

Found this beautiful flower along the hiking/ski trail at Chester Bowl Park in Duluth MN. Flowering on June 22nd.

Posted by: K Chayka
on: 2009-06-22 18:58:05

Beauty is in the eye of the beholder, I think. :) I loathe this plant, myself. It is weedy and invasive and has started taking over the prairie at my favorite park. I look forward to the day when they get a bio agent in there to wipe it out.

Posted by: JB - Randall, Morrison County
on: 2010-07-09 15:49:41

Why is it suggested in the bio-control program to use gloves to hand pull this? Is it poisonous to touch? I pulled some to ID it today and now I'm worrying... We don't have too much, it's just starting to bloom and I plan to hand pull it.

Posted by: JB - Randall, Morrison County
on: 2010-07-09 15:54:16

Nevermind, they must recommend gloves because of the scratchy stems. :) Thanks!

Posted by: K. Chayka
on: 2010-07-09 20:14:51

JB, besides the scratchy stems, I think some people may have a reaction (rash?) to the chemicals in the plant.

Posted by: Anna - Brown County
on: 2010-07-20 10:50:19

We located a thriving population of Spotted Knapweed on 270th avenue in Brown County along the abandoned portion of the road that dips down into the creek valley. (map)

Beautiful Flower. Too bad it's so invasive.

Posted by: Tom - Grand Marais
on: 2010-08-05 23:44:02

I found this plant growing at the edge of our gravel driveway. I agree that the flowers are beautiful--too bad it's a noxious weed! I haven't noticed them before in this area, so I'm wondering where it came from.

Posted by: Rick - Eastern Cass Co. Remer, Longville, Outing
on: 2011-08-17 08:19:30

I believe I found Spotted Knapweed this morning but the leaves on my sample look somewhat different than in the website's photos, is there a similar plant blooming at this time. I'm pretty sure what I have is not a thistle.

Posted by: Rick - Eastern Cass Co. Remer, Longville, Outing
on: 2011-08-19 10:56:25

Upon further investigation I have concluded that it is Spotted Knapweed and I'm unfortunately starting to see more of it along the gravel road I walk along.

Posted by: Mark - Pine Springs Washington Co.
on: 2012-03-09 07:03:59

I have a lot of this in a field behind my house. Have been pulling it out for years.....

Posted by: Kara - Carleton County
on: 2012-07-08 16:06:04

Found this growing along the roadside in Carleton County today. There were just a few plants but sounds like next year there will be more

Posted by: Kathleen - Eagan, Minnesota
on: 2012-07-16 12:51:30

I found several plants blooming during my morning walk along the East side of Dodd Road between Esk Lane and Coventry Parkway in Eagan. It may be city property because it is along a walking/bike path. Is the city required to control invasive species?

Posted by: maia - Lebanon Hills Regional Park, Dakota County
on: 2012-08-18 22:21:25

Found this on the trails by Holland Lake. Apparently bees also mistake this for wild bergamot. Got a great macro photo of a bee on one of these blossoms.

Posted by: Judith - Lake Superior dunes
on: 2014-05-06 12:34:41

I'm in Michigan but want to mention an endangered and federally protected plant on Great Lakes dunes which looks very much like spotted knapweed. It is called Pitcher's Thistle. Please do not pull or poison this plant by mistake.

Posted by: K. Chayka
on: 2014-05-12 19:28:49

While Pitcher's thistle isn't present in Minnesota, it is in Wisconsin so our neighbors there should be aware of this look-alike plant.

Posted by: Kris - Fairview Township
on: 2014-08-07 22:38:32

There is a whole bunch of Spotted Knapweed growing by the side of the road (Cty Rd 77). A whole crop of Lead Plant and Spotted Knapweed. Purple flowers everywhere. Didn't notice that last year. Other purple flowers too.

Posted by: Mayra
on: 2015-07-16 15:36:12

there is a plant near my house that is very similar to knapweed, and it has a purple pink flower... what else is out there that are lookalikes

Posted by: K. Chayka
on: 2015-07-18 07:01:30

Mayra, you should read the Notes section above, that's just below the plant description info. Maybe Mondarda, maybe a thistle.

Posted by: Kimberly - Nobles County, southwest of Adrian
on: 2016-09-28 12:48:04

Infested pasture ~1 acre in size

Posted by: John J - Ponsford,MN
on: 2016-10-11 19:08:25

This plant is actively growing along Red Top Rd and ATV woodland trails on the west side of Bad Medicine Lake which is about 35miles NW of Park Rapids,MN. Thought it an attractive wild flower until I found it online - nasty.

Posted by: Kate - Bloomington
on: 2020-07-27 20:45:50

Found this at Marsh Lake in Bloomington near the archery range. It is definitely making a monoculture. I too was excited to ID a pretty flower until I learned more.

Posted by: gary - Carlton County
on: 2020-08-30 19:44:26

This used to go by the name C. maculata and later C. biebersteinii. I wish someone would make up their minds. Anyway, this plant is all over Carlton County along dry roadsides. There are huge patches on I-35 between Barnum and Carlton. There's a patch on the road where I live and it is now spreading towards my driveway.

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