Carduus acanthoides (Plumeless Thistle)

Plant Info
Also known as: Spiny Plumeless Thistle
Genus:Carduus
Family:Asteraceae (Aster)
Life cycle:biennial
Origin:Eurasia
Status:
  • Invasive - ERADICATE!
  • Noxious Weed
  • Prohibited or Restricted species
Habitat:sun; fields, pastures, roadsides, waste areas, disturbed soil
Bloom season:July - October
Plant height:3 to 6 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: indistinct Cluster type: round

[photo of flowers] Purple flower heads, occasionally white, and smaller than most comparative thistle species, generally 1 inch wide. Flower heads are solitary or in clusters of 2 to 5. The bracts are narrow and spreading with very short spiny tips.

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

[photo of leaves] Leaves are deeply lobed, with lobes further segmented, wavy around the edges, and very spiny. Lower leaves are up to 8 inches long, becoming much shorter in the upper plant. Leaf undersides can be either smooth or have dense, bristly hairs, especially along major veins.

[photo of stems] Stems are densely covered with leafy, spine-tipped “wings” that typically angle downward. Stems may also be bristly hairy and are usually heavily branched in the upper plant.

Notes:

Plumeless Thistle resembles Bull Thistle (Cirsium vulgare), whose flowers are larger and leaves hairier, but is more closely related to Nodding Thistle (Carduus nutans), whose flowers are also larger and have broad showy bracts. The spiniest of all thistles in the state, Plumeless Thistle is on the noxious weed list for Minnesota and a relative new comer here, dispersing rapidly over the last thirty years from the Dakotas to the rest of the state. A common pasture/roadside pest, this species can invade high grade native habitats and is no doubt under-reported in the state. Of note is the MN Weed Advisory Group is recommending this species, currently a Prohibited-Control species, be removed from the noxious weed list because they have determined "infestations [are] primarily caused by human disturbance". The decision seems illogical, since that doesn't make it any less of a pest or threat. According to one source, a mature plant can produce 10,000 seeds. They may disperse within 10 days of flowering and over 90% will germinate. This one is nasty.

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More photos

Photos by K. Chayka taken in Hubbard and Wadena counties. Photos courtesy Peter M. Dziuk, taken at west central, Metro and southeastern MN sites.

Comments

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

Posted by: Andrew - Bemidji Area, Beltrami County
on: 2017-06-17 14:08:48

Noticed this plant for the first time ever this year, but couldn't identify it. Now some have bloomed so I know it is this. A shame that is has reached my area now.

Posted by: Dan S - just east of Cold Spring, Stearns Co.
on: 2017-07-19 16:10:02

I have been dealing with it for at least 6-7 years and didn't know what it was until today. The photo of an infestation could have been taken on my land - I have seen way too many of those, especially encroaching onto my lawn. I have been pretty aggressive in dealing with it - uproot them when I can, and that has reduced it quite a bit. I was cutting them at ground level just this morning. That allows me to mow over them with a lawnmower, which helps a bit. Uprooting is more effective, but some are too big and won't come out without tools.

Posted by: Barb M - Menahga
on: 2017-08-20 10:12:12

Ugh. We have this all over in our field. Especially where we had our burn pile. The spiny leaves make them difficult to remove.

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