Cirsium altissimum (Tall Thistle)

Plant Info
Also known as: Roadside Thistle
Genus:Cirsium
Family:Asteraceae (Aster)
Life cycle:annual, short-lived perennial
Origin:native
Habitat:shade, sun; woods, thickets, fields, roadsides, waste areas
Bloom season:July - September
Plant height:3 to 10 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: panicle

[photo of flowers] Flower heads are few to many at the tips of branching stems in the upper plant. Flowers are purple to pink, rarely white, 1 to 2 inches wide. Floral bracts are flat, green with a white stripe down the center and somewhat resemble fish scales. Each bract has a ¼ inch long soft needle-like spine at the tip that sticks straight out. At the base of these floral bracts surrounding the stalk are several narrow leafy bracts.

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

[photo of leaves] Leaves are alternate, up to 18 inches long and 8 inches wide. Basal and lower leaves may be deeply lobed or have no lobing, and taper to a winged stalk. Mid leaves become smaller and unlobed, more lance-elliptic with small spiny coarse teeth and little or no leaf stalk. Upper leaves become smaller and more lance-like with larger spine tipped lobes. 

[photo of stem and leaf underside] Undersides of leaves are velvety white with fine hairs, the upper surface with stiffer short hairs. Stems are ridged and covered with crisp, bristly hairs but are not spiny; branching is in the upper portions of mature plants.

Notes:

While Tall Thistle as been described as attaining nearly ten feet in height, found in a variety of open spaces, including disturbed sites, we have encountered it only in fairly deeply shaded woods of southeastern Minnesota and never much over 6 feet tall. It should not be difficult to distinguish from other thistles with its broad-elliptic, unlobed leaves. Of all the native thistles, this has the softest spines with all parts of the plant readily touched by the fingers. The floral bracts and white undersides of leaves are much the same as Field Thistle (Cirsium discolor), which has deeply lobed leaves all the way up the stem. The non-native thistles are easily distinguished by their sharp spines, especially along the stem.

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More photos

Photos by K. Chayka and Peter M. Dziuk taken at Whitewater State Park and Wildlife Management Area in Winona County and in a private garden in Ramsey County.

Comments

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

Posted by: Sarah - Southern part of kathio state park
on: 2014-07-26 17:57:03

Large population, many plants on the order of ten feet tall. Is there a way to upload pictures here? It's not in bloom yet but still striking.

Posted by: John - W. St. Paul
on: 2016-06-29 06:51:19

Think I saw it on field trip with the Native Plant Society on June 26, 2016 in wooded areas of the Quarry Park SNA. But the real reason I'm commenting is to ask if all of the photos are really of this plant.

Posted by: K. Chayka
on: 2016-06-30 21:20:21

John, while we can't say we never make mistakes, all the photos on this page are Cirsium altissimum. Was there something different about what you saw at Quarry Park SNA? Perhaps what you saw was C. discolor? C. altissumum has not been recorded in Stearns County but C. discolor has.

Posted by: John - W. St. Paul
on: 2016-08-06 14:11:09

Now that my few thistles are blooming, I see that they do match up with C. discolor. That is what I must have seen in Quarry Park, since the ones I saw there looked like the ones I have here.

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