Yellow flag is a non-native perennial with thick rhizomes from which arise thick, stiff leaves enfolding each other at the base. Plants typically arise as much as 1 meter in height. The leaf blades are as much as 50-90 cm long and 20-35 mm wide and taper to a point at the tip. The leaves are often blue-green in color and the middle leaves are the longest.

The several yellow flowers are found at the apex of the stem. They are large and showy, often with fine purple markings.

Yellow flag is common around streambanks and along the margins of ponds and lakes. It is generally found in areas with permanent shallow water, and at depths less than 0.5 meters.

An introduced species from Europe, yellow flag may be found within its habitat over much of North America.

Yellow flag is a pretty, introduced iris for gardens with moist soils or ponds! Be aware that if you have planted it next to a stream, it will spread from your property onto adjacent streambanks where it crowds out native riparian plants.

It has value as a species for sediment retention and shoreline stabilization. The thick stands of yellow flag provide hiding spots for wildlife.