is a specific kind of: grass.

is a broader term that covers: Agropyron cristatum, crested wheat grass, crested wheatgrass, fairway crested wheat grass | Agropyron repens, couch grass, dog grass, quack grass, quackgrass, quick grass, witch grass, witchgrass | Agropyron subsecundum, bearded wheatgrass | Agropyron smithii, bluestem wheatgrass, western wheatgrass | Agropyron intermedium, Elymus hispidus, intermediate wheatgrass | Agropyron pauciflorum, Agropyron trachycaulum, Elymus trachycaulos, slender wheatgrass.

is a member of: Agropyron, genus Agropyron.