Acorus gramineus, commonly known as Japanese sweet flag, is a perennial herb native to wetlands and shallow water areas in Japan, Korea, and Southeast Asia. It thrives in marshy conditions, along stream banks, and in the margins of ponds and lakes. The plant typically reaches up to 30 cm (12 inches) in height and features long, narrow, slightly curved, grass-like leaves that are bright green and aromatic when crushed. Japanese sweet flag blooms in late spring to early summer, producing inconspicuous greenish-yellow spathes that are often overlooked in favor of its foliage.

Japanese sweet flag is valued for its ability to form dense, evergreen ground cover in wet areas, making it an excellent choice for water gardens, pond edges, and bog gardens. It is also used in traditional medicine and as an ornamental plant in freshwater aquaria. This plant prefers full sun to part shade and requires consistently moist to wet soil conditions. While it can tolerate a range of soil types, it prefers acidic to neutral pH levels. It is propagated by division of the rhizomes, which should be planted in shallow water or very moist soil. Care should be taken as Acorus gramineus can spread aggressively in favorable conditions, potentially becoming invasive.CC BY-SA 4.0