| Sixweeks Threeawn | Aristida | adscensionis | | 4 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |
| Churchmouse Threeawn (dichotoma) | Aristida | dichotoma var. dichotoma | | 43 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |
| Churchmouse Threeawn (curtissii) | Aristida | dichotoma var. curtissii | | 9 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |
| Churchmouse Threeawn | Aristida | dichotoma | | 27 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |
| Woolly Threeawn | Aristida | lanosa | | 19 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |
| Slim-spiked Threeawn (longispica) | Aristida | longespica var. longespica | | 8 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |
| Slim-spiked Threeawn (geniculata) | Aristida | longespica var. geniculata | | 1 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |
| Slim-spiked Threeawn | Aristida | longespica | | 9 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |
| Prairie Threeawn | Aristida | oligantha | | 35 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |
| Arrow-feather Threeawn | Aristida | purpurascens | | 37 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |
| Seaside Threeawn | Aristida | tuberculosa | | 20 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |
| Wand-like Threeawn | Aristida | virgata | | 2 | Grasses | Poaceae | Poales | Magnoliopsida | Plantae |