Above: Plumeless Thistle in Oak Savanna in Madison, Wisconsin (7/2/20).
Plumeless Thistle - Carduus acanthoides (Introduced - naturalized; ecologically invasive)
Plumeless Thistle is a biennial plant. Biennial means that it takes two seasons to complete their life cycle The first season they germinate and create a rosette. The second season they flower and produce seeds.
Plumeless Thistle is restricted in Wisconsin and is considered a ecological threat. It likes disturbed sites such as roadsides and ditch banks and will spread into fields and pastures. Plumeless Thistle can grow from 1'- 4' tall in it's second year.
Plumeless Thistle has pink/purple flower heads are usually about 1/2" - 1" wide.
Blooms July-October.
Above: Plumeless Thistle stem between sidewalk and curb on Tumalo Trail in Madison, Wisconsin (8/16/22). The stems are densely covered with leafy, spine-tipped “wings.”
Above: Plumeless Thistle leaf on shore of Lake Wingra in Vilas Park in Madison, Wisconsin (8/26/22). Leaves are deeply lobed and wavy around the edges with spines at the tips.
Other names: Spiny plumeless thistle, Welted thistle.
Etymology: Acanthoides – resembing a spine or thorn.
For more information on the Plumeless Thistle, visit Wikipedia.
Or, visit the UW-Madison Wisconsin Herbarium online virtual flora website page on Plumeless Thistle.
Or, download a pdf about Plumeless Thistle from the University of Wisconsin Extension's 2017 Weed Identification Series
Or, to eradicate, visit the Wisconsin DNR website on Plumeless Thistle.
Or, to compare it other Biennial thistles (Bull and Musk) download a Biennial Thistle Comparison pdf from the University of Wisconsin Extension's 2017 Weed Identification Series/Biennial Thistle Comparisons
Plumeless Thistle
Carduus acanthoides
Above: Plumeless Thistle in Oak Savanna in Madison, Wisconsin (6/30/22).
Above: Plumeless Thistle by Wingra Boats on shore of Lake Wingra in Madison, Wisconsin (7/11/19).
Above: Plumeless Thistle in Oak Savanna in Madison, Wisconsin (8/4/20).
Above: Plumeless Thistle near sidewalk on Arbor Drive in Madison, Wisconsin (8/26/22).
Above: Plumeless Thistle on shore of Lake Wingra in Vilas Park in Madison, Wisconsin (8/24/22).
Above: Plumeless Thistle between sidewalk and curb on Tumalo Trail in Madison, Wisconsin (8/16/22).
Above: Plumeless Thistle specimen collected on July 17, 1948 in Cross Plains in Dane County, Wisconsin.
Above: Plumeless Thistle specimen (originally wrongly labeled) collected in Dane County on Whalen Road near Fish Hatchery Road in Fitchburg, Wisconsin on July 1, 1995.
Above: Plumeless Thistle.
Above: Video for identifying Plumeless Thistle from the University of Wisconsin Extension.
Above: Plumeless Thistle (Carduus acanthoides) botanical illustration by Swedish botanist Carl Axel Magnus Lindman circa 1917-1926.
Above: Plumeless Thistle (Carduus acanthoides) botanical illustration by Johann Georg Sturm circa 1776.