Irises, with their beautiful, fragrant flowers and sword-shaped leaves, are favorite wildflowers and garden subjects. Eleven species of irises have been recorded as either native or as introduced, surviving outside of cultivation in Missouri. This page is an overview of this group in our state.
Irises are perennials that grow from rhizomes. The leaves are flat and sword-shaped, basal or appearing 2-ranked (alternate, on opposite sides of the stem). The flowering stems are circular in cross-section, unbranched or few-branched.
The flowers are single at the stem tips or in clusters of 2 or 3; a pair of leafy or papery bracts enclose the base of each flower. Each flower has 3 sepals and 3 petals; in most species, the sepals and petals are different in size and position: the sepals spreading and bending downward, the petals erect to spreading.
The fruits are oblong capsules with 3 chambers, the seeds flattened; in blackberry lily (Iris domestica), the seeds are shiny black spheres, appearing as a cluster after the capsule splits open.
Blooms April–July; particular species bloom earlier or later in the season. Blackberry lily blooms July–August.
Gardeners have developed special terminology to describe the parts of irises:
- Standards: Upright petals
- Claws: Narrowed bases of the standards
- Falls: Sepals, which typically droop downward
- Hafts: Narrow, stalklike bases of the falls
- Beard: Line of fuzzy-looking hairs at the base of each fall (not all irises have beards)
- Signal: An upward-pointing yellow and/or white patch of color on falls, positioned where the sepal bends downward, near the mouth of the flower
Species Found in Missouri
Eleven species of irises have been recorded in Missouri as either native (4 species) or as nonnative (introduced and surviving outside of cultivation) (7 species):
Native
- Southern blue flag (I. virginica): scattered statewide. Occurs in a wide variety of wetland situations, sometimes in shallow water. Color ranges from nearly white to deep violet, sometimes in a veined pattern.
- Short-stemmed iris, Lamance iris, zigzag iris (I. brevicaulis): uncommon in Missouri, widely scattered. Occurs in bottomland forests, along streams, ravines, bases of moist slopes. Color can be blue, lavender, or white, with dark veins. Leaves much taller than the flowers; the short stems look somewhat zigzag.
- Crested iris (I. cristata): scattered in the eastern portion of the Ozarks and locally eastward in Scott County (plants in Franklin County are naturalized from cultivation). Upland forests, bluff tops and ledges, sandy stream banks, often on chert or dolomite substrates. It is no more than 12 inches tall, has a distinctive color pattern of light purple, white, yellow, and darker purple, and the sepals (“falls”) have 3 parallel, conspicuous crests.
- Copper iris, red iris (I. fulva): scattered in the Bootheel lowlands. Occurs in swamps, bottomland forests, margins of sloughs, ditches ponds, often in shallow water. Flowers orange, copper, or reddish brown.
Nonnative
- German iris, blue flag (I. germanica): introduced, escaped, naturalized; native to Eurasia. Occurs along roadsides, railroads, old home sites. The most widely cultivated species of iris; iris aficionados have created a multitude of colors in this species. At the base of each flower, the bracts are green and leafy, though they sometimes have papery margins.
- Flag, Dalmation iris, sweet iris (I. pallida): introduced, escaped, scattered sites in Missouri; native to eastern Europe. Occurs along roadsides, railroads, old home sites. Cultivated widely. Less variable than German iris; the flowers are almost always light violet blue. At the base of each flower, the bracts are papery throughout (not green and leafy), grayish white.
- Yellow iris, yellow flag (I. pseudacorus): introduced, escapes, uncommonly naturalized in the southern half of Missouri. Old World native. Commonly cultivated as an emergent aquatic ornamental, occurs in shallow water of shorelines of streams and ponds. Flowers bright yellow, the sepals large and wide, the petals much smaller. In nature, can be an aggressive colonizer and can form large colonies.
- Blackberry lily (I. domestica): introduced, scattered statewide. Native to east Asia. Occurs along roadsides, in old homesites, on bluff edges, and disturbed, brushy areas. Formerly placed in a separate genus, and the flowers do not strongly resemble other iris flowers; the orange flowers, with petals and sepals fairly similar, look more like daylilies; the fruits split open and the clusters of shiny black seeds look like blackberries.
- Dwarf bearded iris (I. pumila): introduced, escapes from cultivation in disturbed areas. Native to Europe. Recorded as naturalized from Boone, Howell, and Washington counties. Widely cultivated, but rarely becomes naturalized in North America. Similar to German iris, with flowers potentially a variety of colors and the sepals with a conspicuous beard of hairs in a line along the upper/inner surface of the basal half of the sepal. Unlike German iris, no part of the plant exceeds 10 inches in height.
- Dwarf iris (I. verna): introduced, rare in nature. Native to the southeastern United States but not to Missouri. Widely cultivated; known to escape cultivation in Crawford County, in a disturbed, grassy area, where plants were spreading from a landscape planting. Leaves to 6 inches tall, flower stalks shorter, flowers usually appear before the leaves lengthen, light violet to blue with a yellow spot on the sepals. Most similar to crested iris, but lacking the crest ridges.
- Turkish iris (I. orientalis): introduced, rare in nature. Apparently native to Turkey and Greece. Known to have escaped in a grassy roadside in Platte County. It is not commonly cultivated in the United States; it likes fairly saline soils, and it is unlikely to spread widely in Missouri. Flowers white, with a yellow area in the middle of each sepal.
Similar species: Other members of the iris family in Missouri are in different genera and do not much resemble the more famous members of genus Iris:
- Celestial lilies or prairie irises (two Missouri species in genus Nemastylis)
- Blue-eyed grasses (four Missouri species in genus Sisyrinchium)
Height: varies with species.
Different species have different habitats and distribution patterns.
Habitat and Conservation
Typical habitats for most native irises are damp, moist soils in bottomlands or the bottoms of ravines, stream banks, the shores of ponds and lakes, sloughs, or wetlands; some species live in shallow water and can be considered emergent aquatics.
The other principal habitat for irises — especially the nonnative species — are roadsides, railroads, and old homesites, disturbed areas where introduced populations persist long after they had been planted.
Status
Native Missouri irises are treasured as wildflowers and are sometimes cultivated in native wildflower gardens. Some wild populations seem to be declining. Never dig plants from natural populations. Acquire them from ethical native wildflower nurseries.
Most nonnative, introduced irises in Missouri are not considered invasive because they are not aggressive; they rarely spread into native habitats or overwhelm native species.
An exception, however, is the nonnative yellow iris (I. pseudacorus), the most aquatic species, which can be an aggressive colonizer in shallow water of shorelines of streams and ponds. It has been declared invasive in some states. It should never be introduced to any native North American habitats.
Human Connections
Many native irises are becoming rarer in the wild, but they are worthy of cultivation as garden ornamentals. Never dig plants from natural settings; purchase them from reputable native wildflower nurseries, which propagate plants sustainably and ethically.
When handled, some iris species may cause mild skin irritation in some people.
Irises have a long history of cultivation worldwide. As far back as the days of ancient Egypt, they have been used as garden ornamentals, in cosmetics, and as medicines.
Essential oils present in the rhizomes of some types of iris have a strong smell similar to that of violets. An extract of I. germanica and I. pallida, called tincture of orris root, has long been used commercially to replicate the smell of violets in perfumes, cosmetic powders, and potpourri. It is also used as an ingredient in gin.
It’s easy to see why irises are so popular as garden ornamentals, and horticulturalists have created a rainbow of colors and flower forms (especially of I. germanica). “Reblooming” cultivars have been developed that bloom in both spring and fall. Some irises have white and green variegated foliage. The American Iris Society keeps a global registry for iris varieties, and iris breeders use creative names for their carefully developed cultivars. Prices may seem high for new iris cultivars, but with care these perennials will flourish, and their rhizomes can be divided and traded with gardening friends.
There is even a group called the Historic Iris Preservation Society, which focuses on preserving the many iris varieties people have cultivated for well over a century. Your great-grandma might have grown and traded hardy, old-fashioned varieties such as ‘Wabash,’ ‘Great Lakes,’ ‘Cardinal,’ ‘Blue Hawaii,’ or ‘Yellow Chalice.’ These are also some of the varieties you may encounter persisting at old homesites, near crumbling house foundations or cisterns.
Culturally, irises are significant across the globe:
- The heraldic fleur-de-lis (a stylized picture of an iris) was the symbol of French royalty, and its presence on the flag of St. Louis symbolizes that city’s French settlement history.
- The fleur-de-lis is also used as a logo for scouting. The three elements represent the three parts of the Scout Promise; also, the upward pointing middle element points like a compass in the true or correct direction, while the two side elements point backward.
- For centuries, painters have loved depicting irises. Van Gogh and Monet famously used them as a subject; they are also a popular subject in Japanese wood block and screen prints and brush paintings, and watercolorists worldwide love to depict irises.
- The state of Louisiana has embraced five native iris species as its official state wildflower, and Tennessee has an iris as a state flower, too.
- Generations of home gardeners have shared and swapped varieties of cultivated irises, adding to their yard's rainbow of colors each spring. In the process, they solidify friendships and contribute to their community's social cohesion.
- Irises are a longtime choice as an enduring grave decoration, and in many old cemeteries, these plants faithfully continue to bloom long after anyone remembers to visit the grave. Even as far away as Iran and Kashmir, irises are commonly planted in graveyards.
The common name, genus name, and Latin family name (Iridaceae) are from the Greek goddess Iris, who conveyed messages from Mount Olympus across the world in the form of a rainbow. Carl Linnaeus, who officially named these plants “iris,” was clearly impressed by the rainbow of colors that irises can display.
Ecosystem Connections
Irises and other plants that grow along streams and in other places prone to flooding help to hold the soil against erosion.
Prominent, colorful veins, or a so-called signal (conspicuous yellow and/or white patch at the throat of the sepal) are visual targets that help pollinating bees (typically bumblebees) know where to seek nectar from the flowers.
An iris’s flower structure forces bees to crawl into the flower beneath one of the three flat, petal-like style arms. As it pushes beneath this structure, the bee rubs previously collected pollen from its back onto a flaplike, down-facing stigmatic lip, fertilizing the flower. Moving further into the flower, the bee rubs against an anther, sticking new pollen to its back.
Thinking further about the floral structure of irises, each iris flower essentially functions like three separate flowers, with each sepal (drooping “fall”) accessed separately by a pollinator. Each sepal is like a tube with its own associated style arm, stigmatic lip, and anther. The three true petals (the upright “standards”) basically function only to attract bees from a greater distance.
Relatives: In addition to native celestial lilies (Nemastylis spp.) and blue-eyed grasses (Sisyrinchium spp.), some other members of the iris family you might be familiar with are common garden or florist flowers: gladioluses (Gladiolus spp.), crocuses (Crocus spp.), and freesias (Freesia spp.).
Several types of insects feed on various parts of iris plants:
- The iris weevil (Mononychus vulpeculus) develops inside the fruit capsules, eating the seeds.
- The larvae of certain leaf miner flies chew squiggly tunnels within the leaves.
- Aphids, thrips, and mealybugs may feed on leaves, rhizomes, or flowers.
- A few species of tiger moths, which eat a variety of plants, may feed on irises as caterpillars.
- The iris borer (Macronoctua onusta), a smoky gray and brown noctuid cutworm moth, is an infamous pest for people who cultivate iris, as its pinkish caterpillars chew down through the leaves and into the rhizomes, often causing bacterial rot.
Although insects that feed on irises are not appreciated by iris gardeners, they are important as food for many different animals, ranging from birds, bats, lizards, and toads to spiders, mantids, assassin bugs, and more.
