Iris ensata, commonly called Japanese iris, is a beardless perennial iris that grows in slowly expanding clumps to 60-120cm tall.
Sword-shaped, linear green leaves (up to 60cm long) have prominent midribs. Huge flowers (typically 10-15cm across) have a distinctively flattened appearance. Cultivars come in single, double and peony flowered forms in a wide range of colours including shades of blue, lavender, violet-red, pink and white. Blooms early to mid summer (later than both Bearded and Siberian iris).
Iris ensata plants are not suitable for standing permanently in water (unlike Louisiana Iris), they require moist but open soil conditions and will rot if left standing in water over winter, so plant at the margins of ponds or streams, or in perennial borders.
Try a clump alongside Sibirica Iris to get a prolonged flowering period.