Above: Tall Thistle in Oak Savanna in Madison, Wisconsin. (8/8/21).
Tall Thistle - Cirsium altissimum
Tall Thistle is a native thistle that can grow anywhere from 3 - 10 feet in height.
The flowers are pink to purple in color and are anywhere from between 1 - 2 inches wide. The floral bracts
are flat, green in color and have a white stripe down the center. There is a 1/4" long spine at the top of each bract that sticks straight out.
At the base of the floral bracts are narrow leafy bracts that unfold and recurve down and up.
The stems are ridged and covered with bristly hairs – but are not spiny.
Blooms: July - September
It is easy to confuse Tall Thistle with Field Thistle (Cirsium discolor) whose flowers look similar (see below).
Tall thistle can grow anywhere from 3 - 10 feet in height and Field Thistle can grow between 3-7 feet in height; however, Tall Thistle has upper leaves that are coarsely toothed and are not lobed; whereas, Field Thistle leaves have long narrow lobes with spines at the tips. Also, if you go the UW-Madison
Wisconsin State Herbarium website page about Tall Thistle - (Cirsium altissimum),
you'll find that many of the specimens that they've collected are hybrids with Cirsium discolor.
Above: Field Thistle flower on left and Tall Thistle flower on the right. Photo taken on August 30, 2022.
Above: Heirloom Tall Thistle leaves in Oak Savanna in Madison, Wisconsin on August 8, 2021. The upper leaves of heirloom Tall Thistle are coarsely toothed and are not lobed. The basal and lower leaves may be deeply lobed or have no lobes. However, Tall Thistle and Field Thistle (Cirsium discolor) often cross pollinate and create hybrids with more unusual shapes. Field Thistle leaves are divided into several narrow lobes (see lower basal leaves below). However, I think even the Tall Thistle example below might be the result of cross pollination.
Above: On the left is a lower leaf of Tall Thistle photographed in the Oak Savanna and on the right is a lower leaf of a Field Thistle leaf photographed in the UW Arboretum's Curtis Prairie in Madison, Wisconsin. Note: Not all Tall Thistles have lobed lower leaves.
For more information on the Tall Thistle (Cirsium altissimum), visit Wikipedia.
Or, visit the UW-Madison Wisconsin State Herbarium website page about Tall Thistle - (Cirsium altissimum) .
Tall Thistle
Cirsium altissimum
Above: Tall Thistle in Oak Savanna in Madison, Wisconsin on August 11, 2021.
Above: A montage of Tall Thistle leaves from plants growing in the Oak Savanna in Madison, Wisconsin. Note the variations in size and shapes of Tall Thistle leaves. (click image to enlarge). It should also be noted that many of the leaves may be hybrids of Tall Thistle and Field Thistle (Cirsium discolor).
Field Thistle leaves are divided into several narrow lobes. Together, with Tall Thistle, they create a collection of leaves that defy classification (for me at least).
One commonality is that the underside of both of their leaves are white and covered in short hairs. The stems of both plants are also hairy with no spines.
Above: Tall Thistle in Oak Savanna growing next to Giant Ragweed in Madison, Wisconsin (8/3/21).
Above: Tall Thistle in Oak Savanna in Madison, Wisconsin on August 24, 2019.
Above: Tall Thistle in Oak Savanna in Madison, Wisconsin on August 21, 2019.
Above: Tall Thistle in Oak Savanna in Madison, Wisconsin on August 14, 2021.
Above: Tall Thistle in Oak Savanna in Madison, Wisconsin on August 22, 2019.
Above: Tall Thistle in Oak Savanna in Madison, Wisconsin on August 25, 2019.
Above: Tall Thistle in Oak Savanna in Madison, Wisconsin on August 14, 2020.
Above: Tall Thistle in Oak Savanna in Madison, Wisconsin on August 3, 2020.
Above: Tall Thistle in Oak Savanna in Madison, Wisconsin on July 30, 2022.
Above: Tall Thistle leaves on same plant in Oak Savanna in Madison, Wisconsin on August 2, 2022.
Above: Tall Thistle in Oak Savanna in Madison, Wisconsin on August 2, 2022.
Above: Tall Thistle in Oak Savanna in Madison, Wisconsin on August 11, 2022.
Above: Field Thistle flower on left and Tall Thistle flower on right.
Above: Tall Thistle specimen collected in 1959 in Barron County, Wisconsin.
Above: Tall Thistle specimen collected in August 31, 1959 in Barron County, Wisconsin.
Above: Tall Thistle (Cirsium altissimum), Field Thistle (Cirsium discolor) hybrid specimen collected in August 31, 1959 in Barron County, Wisconsin.
Above: 1913 Tall Thistle (Cirsium altissimum) drawing.