Acorus gramineus, commonly known as grass-leaf sweet flag, dwarf sedge, Japanese rush, and Japanese sweet flag, is a botanical species belonging to the genus Acorus, native to Japan, Korea in eastern Asia. The plant usually grows in wetlands and shallow water.
This shrubby plant's long, narrow, slightly curved leaves may grow to 30 cm (12 inches) in height. It can grow fully or partially submerged, or in very moist soil, but it will usually only flower when at least partially submerged.
Var. pusillus has slightly shorter, more rigid glossy green leaves, while var. variegatus has longer leaves streaked with yellow.
Acorus gramineus spreads aggressively by rhizome, creating a nearly-seamless groundcover where conditions are favorable, and it is frequently used around the edges of ponds and water gardens, as well as submerged in freshwater aquaria. It can be propagated by dividing the fleshy underwater rhizome and planting the base in shallow water.
In Japan during the Heian period, leaves of the plant were gathered for the Sweet Flag Festival on the fifth day of the fifth month.