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Field Thistle
[Cirsium
discolor (Muhl. ex Willd.) Spreng.]

Location
Description
Flower
Achene

Thistle of ND 

Field thistle has only been documented to occur in extreme eastern North Dakota, although it is quite common in Minnesota and most of eastern North America. Field thistle is found by roadsides, in clearings and openings in wooded areas, and in moist but not marshy locations.

It generally grows 6 to 7 feet tall in North Dakota, but can reach heights up to 10 feet. The tall plant and leaves that resemble oak leaves are two good characteristics for identification of this plant in North Dakota.

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The stems of field thistle are woody, hollow, ribbed and green to green-brown with little pubescence. The plant has many branches, and each branch has a single flower head. The lower leaves are large (10 by 20 inches) and deeply lobed, resembling an oak leaf.

The leaves are light green and shiny on top, pubescent underneath, with very small unimpressive spines.

The leaves get progressively smaller toward the top of the plant. The rosette leaves are similar in shape to stem leaves but grow up to 12 inches long.  

The flowers are pink to lavender, rarely white in color, and the heads are 1.5 to 2 inches wide by 1.5 inches in height.


Each flower head has about eight rows of progressively longer bracts, the outer five rows of which have 0.25 inch long spines bent out and down.

There are numerous leaflike bracts around each flower head. The plant begins flowering in late July through September.

        
Achenes are 0.2 inches long, light brown with darker stripes and a yellow apical collar.
Field thistle is closely related to tall thistle. North Dakota is on the border of the ranges of both species. While they have been found in the state, they are considered uncommon.

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Tall thistle

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