Medium to tall, tufted, rhizomatous plant - slightly branched. Leaves sword shaped, 8 to 25 mm wide, the lower ones often red tinged at the base, without a raised midrib. Flowers 2 to 9, lilac-purple, 70 to 90 mm, the base of the falls yellowish.

Lake shores and water margins.

Flowers June to August.

Perennial.

Widespread but infrequent as a wild flower in Britain.

Uncommon as a wild flower in Leicestershire and Rutland. It was not recorded in the 1979 Flora survey of Leicestershire.