Yellow iris flowers from May to July (6); it reproduces by seeds as well as by vegetative reproduction (3). It is thought by some to be the origin of the 'fleur-de-lis' device used on coats of arms (4). In folk medicine, the rhizome of yellow iris was looked upon as something of a cure-all, being used to treat coughs, convulsions, toothache, diarrhoea, cramp, and as an antidote to poisoning (6). Furthermore, the flowers were used to produce a yellow dye, and the rhizome was used to make black dye (6).
Pale-yellow iris occurs in plant communities associated with water. In its native European range, pale-yellow iris is found in moderately moist meadow communities in northeastern France , hardwood floodplain forest in France , and alkaline peat (fen) communities in Britain . Lists of associated species in Europe are available in these publications: [23,64,86]. Though it is a widespread species in North America, as of this writing (2009), there were few published descriptions of plant communities where pale-yellow iris occurs in North America. The plant community descriptions that follow are divided geographically into the eastern United States and central and western United States.
Eastern United States: In the eastern United States, pale-yellow iris is found in forested wetlands, open wetlands, and in riparian and floodplain communities.
Forested wetlands: In Van Cortland Park, Bronx, New York, pale-yellow iris occurred in a swamp forest dominated by red maple (Acer rubrum), river birch (Betula nigra) and green ash (Fraxinus pennsylvanica) . At the Ipswich River Wildlife Sanctuary in northeastern Massachusetts, pale-yellow iris occurred in both red maple- and shrub-swamp plant communities. Red maple swamps were dominated by red maple, though green ash was an indicator species of this community type. Shrub swamps were comprised of a mixture of wetland herbs and shrubs including sweetgale (Myrica gale), swamp rose (Rosa palustris), hazel alder (Alnus serrulata), and the nonnatives glossy buckthorn (Frangula alnus) and purple loosestrife (Lythrum salicaria) .
Open wetlands: Pale-yellow iris occurred in both natural and constructed tidal freshwater marshes along the Delaware River in New Jersey. Natural marshes in this area were dominated by the perennial species rice cutgrass (Leersia oryzoides), pickerelweed (Pontederia cordata), and/or cattails (Typha spp.) . On Theodore Roosevelt Island in the Potomac River near Washington, DC, pale-yellow iris occurred in a freshwater tidal marsh inundated daily by high tide. The most abundant species in the marsh included green arrow arum (Peltandra virginica), calamus (Acorus calamus), narrow-leaved cattail (Typha angustifolia), and yellow pond-lily (Nuphar lutea) . In Maryland, pale-yellow iris was found in marshes dominated by calamus and in swamps with longbeak arrowhead (Sagittaria australis), Gray's sedge (Carex grayi), shallow sedge (C. lurida), golden ragwort (Packera aurea), marsh blue violet (Viola cucullata), sweet woodreed (Cinna arundinacea), goldenclub (Orontium aquaticum), common winterberry (Ilex verticillata), hazel alder (Alnus serrulata), southern arrowwood (Viburnum dentatum), Virginia sweetspire (Itea virginica), sweetbay (Magnolia virginiana), green ash, and buttonbush (Cephalanthus occidentalis) . In southern West Virginia, pale-yellow iris occurred in fringed sedge (Carex crinita) table wetlands containing a high diversity of mostly native sedges (Carex spp.and Scirpus spp.) and rushes (Juncus spp). These wetlands were often associated with beaver activity .
Riparian and floodplain communities: Pale-yellow iris occurred but was rare in the late 1960s on flats along the Potomac River dominated by bottomland forest species such as sycamore (Platanus occidentalis), boxelder (Acer negundo), American elm (Ulmus americana), and silver maple (A. saccharinum) . At Mt Vernon, Virginia, pale-yellow iris established outside of cultivation in a "low woods" plant community occurring along the Potomac River, in lower reaches of small streams, and along edges of an infilled marsh. Common species in this community included boxelder, red maple, river birch, green ash, and sycamore .
Pale-yellow iris was an uncommon species on floodplain and lowland "woodlands" on the edges of swamps in Maryland. These areas were dominated by swamp white oak (Quercus bicolor), willow oak (Q. phellos), pin oak (Q. palustris), Shumard oak (Q. shumardii), sweetgum (Liquidambar styraciflua), and red maple .
In southern West Virginia, pale-yellow iris occurred in both floodplain and riparian plant communities. On wooded upper beach areas, pale-yellow iris occurred in sycamore-river birch forest. This community was often inundated with high water, and substrate varied from sand and mud flats to gravel to large cobble. In this region, pale-yellow iris also occurred in American eelgrass-pondweed (Vallisneria americana-Potamogeton spp.) instream wetlands, establishing from shoreline to well within the streambed. It was also found in black willow (Salix nigra)-river birch communities within tributary streambeds and on riverside beach areas. Inundation with high water was common. Substrates included cobblestone, gravel, or sand. Pale-yellow iris also occurred in Lizard's tail (Saururus cernuus) silt accumulations in shallow stretches of slow moving water, often associated with backwater channels and beaver activity .
Central and western United States: As of 2009, the only published descriptions of plant communities with pale-yellow iris in the central and western United States were broadleaf cattail (T. latifolia) communities. Near Duluth, Minnesota, pale-yellow iris appeared the third season after the construction of a sandbar. Dominant plants included sandbar willow (Salix interior) and broadleaf cattail . In Montana, pale-yellow iris occurred in "extensive" stands by itself and intermixed with broadleaf cattail and other aquatic plants . In Sonoma County, California, pale-yellow iris occurred in a marsh with broadleaf cattail, broadleaf arrowhead (Sagittaria latifolia), Cusick's sedge (Carex cusickii), awlfruit sedge (C. stipata), and the nonnative yellow marsh marigold (Caltha palustris) .
The yellow iris is a robust plant with beautiful bright yellow flowers (4). The roots and bulbs are thick and fleshy, and the narrow sword-shaped leaves are bluish-green with a prominent mid-rib (5). Between 4 and 12 large, showy flowers are borne on a somewhat flattened stem (5); they vary in colour from pale yellow to almost orange (2). An alternative name for this species is 'segg', which derives from an Anglo-Saxon word meaning 'short sword', and refers to the shape of the leaves (4). The fluttering of the flowers was thought to resemble flags blowing in the breeze, hence the name 'yellow flag' (6).
Pale-yellow iris seeds are dispersed by water  (reviews by [35,90]). Seeds float on the water surface in fall and early spring  and germinate along shorelines when water recedes (reviews by [35,78]). In laboratory tests, 100% of pale-yellow iris seeds floated during their 1st week, and at least 95% continued to float for 2 months (review by ). In other buoyancy tests, 25% of pale-yellow iris seeds were still floating 354 days after placement in water, and 10% were still floating after 429 days, the longest time period of any of the species tested .
The preference is full or partial sun, wet to moist conditions, and rich soil containing organic matter or muck. This robust iris is easy to grow if it receives enough moisture. It is able to survive occasional dry spells.
Among the introduced Iris spp., Yellow Iris is the only one that can be considered invasive (or at least potentially invasive). Sometimes the commonly cultivated Iris × germanica (Bearded Iris) will escape, but it doesn't appear to be nearly as aggressive. Another introduced species, Iris flavescens (Bearded Yellow Iris), also has yellow flowers, but it rarely escapes. However, like the Bearded Iris, the Bearded Yellow Iris has patches of hair on its sepals. In contrast, Yellow Iris never has hair on its sepals. In this regard, it is similar to the native Iris virginica shrevei (Blue Flag Iris), although the latter has blue-violet flowers. Yellow Iris differs from the preceding Iris spp. by the small size of its erect petals they are even smaller than the petaloid styles and rather inconspicuous.
Common in wet habitats including wet meadows, wet woods, fens, wet dune-slacks, and the edges of watercourses, lakes and ponds. In the north and west of Britain it may also be found alongside coastal streams, on raised beaches, saltmarsh and shingle. It has in many cases been planted in the wild and escaped from gardens (3).