It appears that different authorities don't agree on the classification of specimens, and have produced different distribution maps for this species within the state. For example, Mohlenbrock (1986, 2001) and the ILPIN database restict the distribution of Euthamia gymnospermoides to the northern and western areas of the state, while Jones and Fuller (1955) and A.G. Jones (1973) state that this species occurs in other parts of the state, where it is supposed to be rather common. In my experience, these latter authorities are correct, as I have often encountered this species in east-central Illinois in prairie remnants along railroads. The Plains Grass-Leaved Goldenrod is often confused with Euthamia graminifolia (Grass-Leaved Goldenrod), and therefore its distribution within the state has been seriously underestimated. To distinguish these two species, it is necessary to count the number of florets in a sample of flowerheads. The Plains Grass-Leaved Goldenrod has 15-19 florets per flowerhead, while the Grass-Leaved Goldenrod has 20-35 florets per flowerhead (counting ray and disk florets together). Other differences between these two species include the following: 1) the former species has stems that are always hairless, while there are usually lines of hairs along the stems of the latter; 2) the former species has leaves that are more slender, usually with a single prominent vein, while the latter has leaves that usually have 3 prominent veins; and 3) the former species is usually shorter and bushier in appearance, while the latter is tall and slender. The Plains Grass-Leaved Goldenrod is also similar in appearance to Euthamia tenuifolia (Slender Grass-Leaved Goldenrod). However, this latter species is restricted to sandy prairies and dunes near Lake Michigan in Illinois. Its leaves are even more slender than the preceding Euthamia spp., and its flowerheads don't aggregrate together into the sessile clusters of the Plains Grass-Leaved Goldenrod, as described above. According to Jones and Fuller, they occur individually on separate pedicels. Older scientific names for the Plains Grass-Leaved Goldenrod are Euthamia meadia and Solidago meadia.