This guide was compiled to provide an aid for the rapid identification of the more common pest and non-pest thistle species in South Dakota. Because of the great expense of managing and controlling invasive thistles in rangelands, pastures, and croplands, it is essential to be accurate in the identification of any species at hand. The recognition of native species not only helps maintain local biodiversity, but also prevents wasted effort, controls costs, and minimizes herbicide use and chemical pollution. It should be noted that native thistles are important both as floral resources for native pollinating insects and as seed sources for birds. To a certain degree, invasive thistle species are also important in these regards, but their negative impact to native communities outweighs their supplementary value.
There are 11 species of plants in South Dakota commonly called thistle. This does not include sow thistle (Sonchus spp.) or Russian thistle (Salsola spp.), neither of which is closely related to true thistles. Six of these 11 are native species and are natural components of prairie, meadow, or woodland habitats. The remaining five are exotic species from Europe and Asia that were introduced to the U.S. The exotics are invasive weeds and have significant economic impact on crop and livestock production, native biological community stability, and recreation. This guide is useful for discriminating between the five native and five exotic species most commonly found in South Dakota.
SDSU Cooperative Extension Service
Johnson, Paul J.; Larson, Gary E.; and Deneke, Darrell, "A Guide to the Common Native and Exotic Thistles of South Dakota" (2008). SDSU Extension Special Series. 21.