The Louisiana iris was designated the official state wildflower in 1990 (the state flower is the magnolia blossom). The iris has sword-like foliage and grows to 5 or 6 feet. It has a wider color range than any other iris (blue, purple, yellow, pink, white, and shades of brownish red).

The Louisiana iris grows wild mostly in marshy locations in coastal Louisiana, and for about 100 miles inland, but also adapts to almost any climate and is popular as an ornamental. The great abundance of wild iris blooming in the spring has been an inspiration for artists in New Orleans.

Source:

State Wildflower: Louisiana Secretary of State
Louisiana Iris: Aggie Horticulture - Texas A & M University

Links:

Louisiana Iris: by Rich Sacher - Victorian Adventure
Growing Information: Society for Louisiana Irises
State Flowers - 50 States List
National Flower