Blue flag and other irises often are perennial plants that are found in shallow water along shorelines and in wet areas. Stems grow in clusters from the base, usually single or double-branched, and can be from less than a foot tall to over 3 feet. Leaves are sword-like or blade-like. Flowers are on an elongated stem that usually rises above the leaves. Six-petaled iris-like flowers (actually 3 petals and 3 sepals) can be bluish-purple to violet in blue flag to white, yellow, or copper-colored in other iris species. Flowers are fragrant. Irises have shallow roots and can spread from the roots.
This plant occurs in marshes, wet savannas and pinelands, shallow water in ditches, and in soggy meadows.