Field Thistle- Cirsium discolor

Above: Eastern Tiger Swallowtail butterfly on Field Thistle near the Arborteum Visitor's Center in Madison, Wisconsin (8/16/20).

Field Thistle - Cirsium discolor

Field Thistle is a native thistle that can grow anywhere from 3 - 7 feet in height.

The flowers are pink to lavender in color (sometimes white) 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 has that sticks straight out.

The stems are ridged and covered with bristly hairs – but are not spiny.

Blooms: July - October

It is easy to confuse Field Thistle with Tall Thistle (Cirsium altissimum) 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.

Other names include: Pasture thistle, Prairie thistle.

Above: Mid-stalk Field Thistle leaves in the UW Arborteum near the Seminole Highway entrance in Madison, Wisconsin on August 15, 2022. Field Thistle leaves are divided into several narrow lobe. They look somewhat similar to Bull Thistle leaves (see below); however, the underside of Field Thistle leaves have a whitish fuzz; whereas, Bull Thistle leaves are green on both sides.

Above: On the left is a lower leaf of a Field Thistle leaf photographed in the UW Arboretum's Curtis Prairie in Madison, Wisconsin and on the right is a Bull Thistle leaf on the shore of Lake Wingra in Vilas Park on August 15, 2022. They are both deep lobed with spiny tips. However, the underside of a Field Thistle leaf is whitish in color; whereas, Bull Thistle leaves are green on both sides. Also, Field Thistles stalks are hairy (like Tall Thistle) and DO NOT have spines; whereas, Bull Thistles stalks DO have leaf-winged spines.

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Thistle

by Scottish author, Elizabeth Gordon

Sir Thistle is a Scotchman bluff,

His manners are a tifle rough;

You find him everywhere you go;

He travels on the wind, you know.

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For more information on the Field Thistle (Cirsium discolor), visit Wikipedia.

Or, visit the UW-Madison Wisconsin State Herbarium website page about Field Thistle - (Cirsium discolor) .

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