This common grass is one of the annual Panicum sp. in Illinois. Other species in this group include Panicum capillare (Witch Grass) and the introduced Panicum milaceum (Broomcorn Millet). The latter differ from Fall Panicum by their conspicuously hairy sheaths. A large specimen of Fall Panicum could be confused with Panicum virgatum (Switch Grass), which has hairless sheaths. Switch Grass is a perennial that is often found in tallgrass prairies. It has longer spikelets (about 4-5 mm.) and longer first glumes (about one-half the length of the spikelets) than Fall Panicum, which has spikelets less than 3.5 mm. in length and first glumes about one-fourth the length of the spikelets. Because Fall Panicum is rather variable across its range, different varieties have been identified: var. dichotomiflorum, var. geniculatum, and var. puritanorum. The first two varieties are occasional to common in Illinois and they often intergrade in the field. The typical variety has an inflorescence that is long-exerted from the uppermost leaf and it is less likely to be tufted at the base with inflated sheaths and swollen nodes than var. geniculatum. In contrast, var. puritanorum has smaller spikelets (about 2 mm. long) and more narrow leaves (up to 1/3" across) than either of the preceding varieties. So far, it has been found only in Cook County.