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yellow iris (Iris pseudacorus)




















pale-yellow iris
paleyellow iris
water flag
yellow iris
yellow flag
yellow flag iris


SCIENTIFIC SYNONYMS: There are no scientific synonyms for Iris
pseudacorus L.


CONFIRMATION STATUS: Pending confirmation.


TAXONOMY: The currently accepted scientific name for yellow iris is
Iris pseudacorus L. Several cultivars have been developed from Iris
pseudacorus. For the Nature Guide, only the original Iris pseudacorus is


NATIVE STATUS: Introduced, United States and Canada.




Habit: Yellow iris is a perennial forb often forming dense stands of robust

plants. Single or multiple flowering stems are 20 to 39 inches (50-100 cm)

tall, usually shorter than or equaling leaves.


Leaves: The few to several leaves of yellow iris are stiff and erect, linear,

and 10 to 35 inches (25-90 cm) long. Leaves flattened, arising in a fan

from the soil. They have a raised midrib and the general form is sword-

like, fine-pointed. The upper portion of leaves may arch.


Flowers: Flowers on erect stalks (peduncles) 3-4 feet in height. Flowers

are bisexual, large (3 to 4 inches wide), showy, pale to deep yellow, (the

only yellow iris in the U.S.), sometimes cream-colored with several flowers

on each stem. Plants take 3 years to mature before flowering. Flowers have
6 clawed perianth segments including 3 large downward-spreading sepals
and 3 smaller erect petals. On each flower sepal (yellow, large and petal-
looking) are patterns of delicate light-brownish to purple veins or flecks.


Fruit/Seeds: Yellow iris fruits are large cylindrical, glossy green 6-angled capsules, 2 to 4 inches (5-9 cm) long. The dark brown, smooth, disk-like

seeds are closely packed into 3 rows within the capsule. Seeds have a hard

seed coat beneath which there is a gas space, allowing seeds to float in



Roots: Yellow iris has stout rhizomes that are 0.4 to 2 inches (1-4 cm) in

diameter. Yellow iris invests heavily in root development, particularly as

a young plant, allowing it to establish in habitats with fluctuating water

levels. Roots are usually 4 to 8 inches (10-20 cm) long but can be up to

12 inches (30 cm) long.


REGENERATION PROCESS: Yellow iris regenerates vegetatively
via rhizomes . When plants reach about 10 years of age rhizomes fragment
and contribute to new plant establishment. Thick rhizomes tend to prevent
mixing of adjacent clones, but often 2 or 3 clones may lie on top of each
other, with the bottom rhizome occurring at a depth of about 4 inches (10
cm). Up to several hundred flowering plants may be connected rhizomat-
ously. Rhizomes may grow over the soil, rocks, or as mats floating in water.


HABITAT TYPES: In the eastern United States, yellow iris is found in

forested wetlands, open wetlands, and in riparian and floodplain com-



SITE CHARACTERISTICS: Yellow iris needs moisture to establish
and survive. Consequently, it often occurs on the wet edges of lakes,

ponds, rivers, and streams. Yellow iris also occurs in marshes, tidal marsh-

es, wetlands, swamps , swampy woodlands, open woods, wood edges, and
glacial potholes. Yellow iris occurs on beach swales and rocky coastal
shorelines. Yellow iris is associated with human-made structures such
as ditches, irrigation canal banks, constructed gravel trails through wet-
lands, man-made pools, meadows, wet pastures, and other disturbed sites.

Yellow iris is found in fresh, brackish and salt water.


Disturbances such as flooding play a key role in yellow iris establishment. Rhizomes may break off during floods and are moved to new loca- tions

by water. Floods may also transport yellow iris seeds. Yellow iris usually

grows on water-deposited substrates such as silt, sand, gravel , and cobbles.

One review notes that yellow iris may be found on "rocky" sites. It is

associated with calcareous, sandy loams, clay loams, and other loamy or

clayey soils derived from sandstone and schist in its native range.


Yellow iris grows best in full sun to partial shade and is intolerant of deep

shade. Low light may limit seedling establishment but not necessarily
mature pale-yellow iris growth.


SEASONAL DEVELOPMENT: Pale-yellow iris flowers from late May
to early July in North America.


GENERAL DISTRIBUTION: Yellow iris is native to Europe, northern

Africa, and temperate Asia. A valued horticultural plant, yellow iris was

brought to North America and escaped cultivation, often spreading down

watercourses or washing downstream in floods. A review of early floras

documented yellow iris in Virginia as early as 1771. Yellow iris is widely

distributed across most of the United States and Canada. It occurs in almost

every state, with the exceptions of North Dakota, South Dakota, Iowa,

Wyoming, Colorado, Oklahoma, New Mexico, and Arizona.




IMPORTANCE AND USES: Yellow iris is generally of little value
to wildlife or livestock. Pale-yellow iris is considered poisonous due to
large amounts of glycosides found in foliage and rhizomes.


The tendency for yellow iris to grow in large, radially spreading clones
allows it to form dense stands that may replace native vegetation, includ-

ing 2 native irises in Massachusetts and characteristic California marsh

plants such as cattails (Typha spp.) Yellow iris may also reduce habitat
needed by waterfowl and fish, including several important salmon species.
Yellow iris may also reduce available forage for livestock.


Yellow iris has been used as a rehabilitation plant to reduce bacterial
loads, absorb heavy metals from contaminated water, and provide erosion
control. Yellow iris was smoked by people during World War II and
has been used as a diuretic, to prevent gas, and to treat eczema.



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