I. pseudacorus is one of two Iris species native to Great Britain, the other being the Stinking Iris (Iris foetidissima). It is an extremely vigorous, hardy plant and has become an invasive plant in some areas. These plants grow best along or in ponds or streams.

Yellow Flag Iris have yellow flowers (of course) with brown colored veins. The blooms are 1½-2 inches wide and open in early to mid-summer.