Description: This native perennial plant is 2-3' tall. It produces clumps of vertical leaves that are sword-shaped and up to 2½' tall. These leaves are pale bluish green to green and hairless. An individual leaf is up to 1" across near the base, with smooth margins and parallel veins, and tapering to a point.
The flowering stalks are sparingly
branched and up to 3' tall. Each stalk produces a few leafy bracts and 1-3
flowers. The violet-blue flowers are up to 3½" across, consisting of 3
sepals and 3 petals. The sepals are larger than the petals and spread outward
from the center of the flower. Each sepal is divided into a lower and upper
lip. The lower lip functions as a landing pad for visiting insects, and has
fine purple lines spanning a white or violet-blue background. There is a patch
of bright yellow at the base of this lower lip, and there are no hairs. The
upper lip of the sepal is shorter and flares upward towards its tip. The petals
are held more erect and provide the flower with vertical interest. They are
violet-blue and often have fine lines that are a darker shade of color. The
blooming period is late spring to early summer, and lasts about a month for a
colony of plants, although individual blossums are short-lived. The flowers are
often fragrant. Each flower is replaced by an oblong capsule with 3 blunt
angles. This capsule is about 1½–2" long and ½" across, and
contains rows of tightly stacked seeds. The root system consists of fleshy
rhizomes with abundant coarse roots. This plant often forms colonies by
vegetative reproduction.
Cultivation: The preference is wet to moist
conditions, partial to full sun, and a rich organic soil. In light shade, this
plant often fails to flower, and it tends to decline in abundance if conditions
become too dry. The foliage is rarely bothered by disease or insects. To
maintain the viability of the seeds, they should not be allowed to dry out
– store them with some moist sand.
Range & Habitat: Blue Flag Iris is
surprisingly common in most areas of Illinois, except for some southern and
western counties where it is uncommon or absent. Habitats include wet to moist
black soil prairies, sunny floodplains along rivers, edges of ponds and lakes,
swamps, fens, bogs, ditches and low-lying ground along railroads and roadsides.
Declining remnant populations can be found in some woodland areas where fire
has been surpressed.
Faunal Associations: Nectar-seeking
bumblebees are the most important pollinators of the flowers. Butterflies and
skippers are less common nectar-seeking visitors, but they are not effective at
cross-pollination. Short-tongued Halictid bees and various beetles may also
visit the flowers for pollen, but they are not effective pollinators either.
Mammalian herbivores rarely bother this plant because the foliage and
rootstocks are somewhat toxic, causing irritation of the gastrointestinal
tract.
Photographic Location: The
photograph was taken at a moist remnant prairie along an abandoned railroad
near Urbana, Illinois.
Comments: This attractive plant is more
typical of wetlands than true prairies, but it sometimes spreads into adjacent
sunny areas that are moist. Cultivars of Iris X germanica (German Iris)
have beards (numerous hairs) near the base of their sepals, while the Blue Flag
Iris is beardless. The Blue Flag Iris resembles another native species, Iris
brevicaulis (Blue Marsh Iris), but this latter species has shorter leaves
and 6-angled capsules. Another scientific name for the Blue Flag Iris is
Iris shrevei; a more specific common name is the Southern Blue Flag
Iris.