Centaurea stoebe (Spotted Knapweed)
| Also known as: | |
|---|---|
| Genus: | Centaurea |
| Family: | Asteraceae (Aster) |
| Life cycle: | biennial, short-lived perennial |
| Origin: | Europe |
| Status: |
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| 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): |  |
| National distribution (click map to enlarge): |  |
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Detailed Information
Flower: 
![[photo of flowers]](/udata/r9ndp23q/pd/centaurea-stoebe-13.jpg)
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]](/udata/r9ndp23q/pd/centaurea-stoebe-1.jpg)
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:
![[photo of mid stem leaves]](/udata/r9ndp23q/purple/spotted-knapweed_0905_091033.jpg)
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:
![[photo of seed heads]](/udata/r9ndp23q/pd/centaurea-stoebe-14.jpg)
Flower heads become seed heads about ½ inch long.
![[photo of seeds]](/udata/r9ndp23q/pd/centaurea-stoebe-seeds-15.jpg)
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
Spotted Knapweed plant
Spotted Knapweed plants
Spotted Knapweed plants
an infestation of Spotted Knapweed
emerging in spring
first year rosette
more leaves
more flowers
a white Spotted Knapweed flower
comparison of Centaurea stoebe and C. nigrescens phyllaries
Spotted Knapweed plant
Spotted Knapweed plants
Spotted Knapweed plants
an infestation of Spotted Knapweed
emerging in spring
first year rosette
more leaves
more flowers
a white Spotted Knapweed flower
comparison of Centaurea stoebe and C. nigrescens phyllariesPhotos 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?
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.
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.
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.
on: 2010-07-09 15:54:16
Nevermind, they must recommend gloves because of the scratchy stems. :) Thanks!
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.
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. Beautiful Flower. Too bad it's so invasive.
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.
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.
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.
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.....
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
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?
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.
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.
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.
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.
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
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.
on: 2016-09-28 12:48:04
Infested pasture ~1 acre in size
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.
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.
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.
on: 2022-06-09 10:52:31
Spotted knapweed is a very common invasive species in Meeker County. It is all through the road ditches, on private land, and on public land. I know of a few biological control weevil releases (seed head & root), but it is still a wide spread problem. I mention this because I noticed that Meeker County isn't highlighted on either of the distribution maps.
on: 2022-06-09 11:00:24
Marsha, a lot of weeds are under-reported in the state. The best way to rectify this is to submit a specimen to the Bell Herbarium, then it becomes part of the official record. In lieu of that, the distant second best thing is to report it on EDDMapS.
on: 2022-07-04 20:38:58
Today I found a small beetle on Centaurea macrocephala, a relative of knapweed but with yellow flowers. I think the beetle is in the genus Larinus which has been introduced to control knapweed. It is tiny, brown with small dark spots. Since my Centaurea macrocephala (well-behaved compared to other knapweeds) is far from patches of the spotted knapweed it seems to me that they may be residing on these, too. Well, here's wishing them all the success!
on: 2022-07-15 13:51:05
What can I spray to get rid of it
on: 2022-07-18 09:51:18
Dean, refer to the MN Dept of Ag fact sheet for control measure.
on: 2022-07-26 08:41:46
There are a lot of these plants among the wildflowers at Frogtown.
on: 2023-07-03 20:31:44
I used a wildflower mix in my small pollinator garden. The plant app identified a purple flowering plant as spotted knapweed. It was confirmed by the DNR who recommended digging out the tap root. Wear gloves and long sleeves when removing it as it can irritate your skin.
on: 2023-07-19 08:20:55
I loathe this plant, too. It's everywhere in my area. My friend once brought a vase filled with spotted knapweed flowers to a meeting - she thought the "ditch weeds" were really pretty! I'm afraid this species is considered a pretty wildflower and desirable because butterflies visit it. I am busy reported observations to EDDMapS, but don't really have much hope that will do much.
on: 2024-02-10 03:50:39
I can see by a previous comment,I had spotted knapweed growing about 10 yrs ago in my ditch, sandy/loamy soil. I tried picking off buds before blooming, but it's too much now. They will be putting in a trail in this area next summer, so, although I'll lose many of the desired plants for the rusty patched bee, maybe it will eliminate the spotted knapweed.