Yellow flag iris

(Iris pseudacorus)

Yellow flag iris is an herbaceous perennial, semi-aquatic, obligate wetland species, originally from Eurasia and northern Africa. Plants are found in areas such as stream edges, rivers, lakes, and ponds and form dense, robust monocultures that expand aggressively and outcompete native vegetation. Yellow flag reproduces mostly through vegetative means, through the spread of large clumps of rhizomes in water but can also reproduce by seed. Plants typically produce up to 120 seeds per pod which can remain buoyant and float for up to two months. Leaves are long, flat, and cattail-like, usually blue-green in color, broad, pointed at the tips, and originating from a single point. In cross-section, the base of yellow flag iris is flattened compared to the round base of cattails. The plant grows 3 to 6 feet in height, and flowers are yellow with three petals and three sepals. Yellow flag iris is the only yellow iris found in wetlands in Colorado.

Yellow flag iris fact sheet


Colorado counties map of Yellow Flag Iris Sites in 2023.