Thistle, Plumeless

Carduus acanthoides requires a special mention here, as it has been found growing in the disturbed logging areas near Little Bass Lake, and is quite ubiquitous in Minnesota. It is an INVASIVE species that should be eradicated, and on the noxious weed list for Minnesota. Legal status: Prohibited-Control.

Plumeless thistle is the spiniest of all the nonnative thistles in Minnesota, and the ‘plumeless’ reference comes from the fact that , In its 2nd year it can bolt to up to 6 feet tall, clustered with flowers. Flower heads are deep pink to purple in color and a bit smaller than other exotic thistles at 1″ across. Flower head bracts are narrow and spread outward with very short, spiny tips, not as noticeable as the bracts of a plant it resembles, the nodding thistle. Looking down at the top of the plumeless thistle flower, the effect is of a very round and full bloom. Stems are completely covered in leafy spine-tipped wings. Leaves are deeply lobed and spiny as well, but hairless on the upper side unlike the noxious bull thistle which this plant resembles. Bull thistles, however, have hairy leaves on both sides, and larger, more bulbous flower heads. Plumeless thistle is also often mistaken for nodding thistle — another noxious weed. The difference here is that nodding thistle also has larger flower heads starting at 2″ across, with an easy ID of very showy pink bracts extending all around the flower.

Plumeless thistle can be a nasty spreader once it goes to seed. Unlike other thistles that have ‘plumes’ of long white hairs to help the attached seeds disperse into the wind, plumeless thistle flowers reproduce by plumeless seeds falling a short distance from the plant. The seeds can remain viable in the soil for 10 years.