Sweet flag are 2 species of rhizomatous perennials, often found in swamps, shallow water and wet places. Linear, scented leaves and rhizomes. The foliage is used in Chinese herbal medicine and has been an ingredient in sacred oils for anointing altars. Acorus, deemed a primitive genus of monocots (grasses and grass-like plants) and the only genus in Acoraceae.
As with any emergent plant, sweet flags create refuges in shallow water for invertebrates from predation by fish, and secluded nest sites for birds such as moorhens. While nowadays A. calamus is found widely in the wild in the UK, this non-native species poses relatively little risk to natural habitats: the garden form is sterile and cannot therefore spread by seed.