Iris is a genus of 260–300 species of flowering plants with showy flowers. It takes its name from the Greek word for a rainbow, which is also the name for the Greek goddess of the rainbow, Iris. Some authors state that the name refers to the wide variety of flower colors found among the many species. As well as being the scientific name, iris is also widely used as a common name for all Iris species, as well as some belonging to other closely related genera. A common name for some species is 'flags', while the plants of the subgenus Scorpiris are widely known as 'junos', particularly in horticulture. It is a popular garden flower.
The often-segregated, monotypic genera Belamcanda (blackberry lily, I. domestica), Hermodactylus (snake's head iris, I. tuberosa), and Pardanthopsis (vesper iris, I. dichotoma) are currently included in Iris.
Three Iris varieties are used in the Iris flower data set outlined by Ronald Fisher in his 1936 paper The use of multiple measurements in taxonomic problems as an example of linear discriminant analysis.
Irises are perennial plants, growing from creeping rhizomes (rhizomatous irises) or, in drier climates, from bulbs (bulbous irises). They have long, erect flowering stems which may be simple or branched, solid or hollow, and flattened or have a circular cross-section. The rhizomatous species usually have 3–10 basal sword-shaped leaves growing in dense clumps. The bulbous species have cylindrical, basal leaves.
The inflorescences are in the shape of a fan and contain one or more symmetrical six-lobed flowers. These grow on a pedicel or peduncle. The three sepals, which are usually spreading or droop downwards, are referred to as "falls". They expand from their narrow base (the "claw" or "haft" ), into a broader expanded portion ("limb" or "blade") and can be adorned with veining, lines or dots. In the centre of the blade, some of the rhizomatous irises have a "beard" (a tuft of short upright extensions growing in its midline), which are the plant's filaments.
The three, sometimes reduced, petals stand upright, partly behind the sepal bases. They are called "standards". Some smaller iris species have all six lobes pointing straight outwards, but generally limb and standards differ markedly in appearance. They are united at their base into a floral tube that lies above the ovary (known as an epigynous or inferior ovary). The styles divide towards the apex into petaloid branches; this is significant in pollination.
The iris flower is of interest as an example of the relation between flowering plants and pollinating insects. The shape of the flower and the position of the pollen-receiving and stigmatic surfaces on the outer petals form a landing-stage for a flying insect, which in probing for nectar, will first come into contact with the perianth, then with the stigmatic stamens in one whorled surface which is borne on an ovary formed of three carpels. The shelf-like transverse projection on the inner whorled underside of the stamens is beneath the overarching style arm below the stigma, so that the insect comes in contact with its pollen-covered surface only after passing the stigma; in backing out of the flower it will come in contact only with the non-receptive lower face of the stigma. Thus, an insect bearing pollen from one flower will, in entering a second, deposit the pollen on the stigma; in backing out of a flower, the pollen which it bears will not be rubbed off on the stigma of the same flower.
Iris is the largest genus of the family Iridaceae with up to 300 species – many of them natural hybrids. Modern classifications, starting with Dykes (1913), have subdivided them. Dykes referred to the major subgroupings as sections. Subsequent authors such as Lawrence (1953) and Rodionenko (1987) have generally called them subgenera, while essentially retaining Dykes' groupings, using six subgenera further divided into twelve sections. Of these, section Limneris (subgenus Limneris) was further divided into sixteen series. Like some older sources, Rodionenko moved some of the bulbous subgenera (Xiphium, Scorpiris and Hermodactyloides) into separate genera (Xiphion, Juno and Iridodictyum respectively), but this has not been accepted by later writers such as Mathew (1989), although the latter kept Hermodactylus as a distinct genus, to include Hermodactylus tuberosus, now returned to Hermodactyloides as Iris tuberosa.
Rodionenko also reduced the number of sections in subgenus Iris, from six to two, depending on the presence (Hexapogon) or absence (Iris) of arils on the seeds, referred to as arilate or nonarilate. Taylor (1976) provides arguments for not including all arilate species in Hexapogon.
In general, modern classifications usually recognise six subgenera, of which five are restricted to the Old World; the sixth (subgenus Limniris) has a Holarctic distribution. The two largest subgenera are further divided into sections.
- Iris (Bearded rhizomatous irises)
- Limniris (Beardless rhizomatous irises)
- Xiphium (Smooth-bulbed bulbous irises: Formerly genus Xiphion)
- Nepalensis (Bulbous irises: Formerly genus Junopsis)
- Scorpiris (Smooth-bulbed bulbous irises: Formerly genus Juno)
- Hermodactyloides (Reticulate-bulbed bulbous irises: Formerly genus Iridodictyum)
Sections, series and species
Distribution and habitat
Nearly all species are found in temperate Northern hemisphere zones, from Europe to Asia and across North America. Although diverse in ecology, Iris is predominantly found in dry, semi-desert, or colder rocky mountainous areas, other habitats include grassy slopes, meadowlands, bogs and riverbanks.
Iris is extensively grown as ornamental plant in home and botanical gardens. Presby Memorial Iris Gardens in New Jersey, for example, is a living iris museum with over 10,000 plants, while in Europe the most famous iris garden is arguably the Giardino dell'Iris in Florence (Italy) which every year hosts a well attended iris breeders' competition. Irises, especially the multitude of bearded types, feature regularly in shows such as the Chelsea Flower Show.
For garden cultivation, iris classification differs from taxonomic classification. Garden iris are classed as either bulb iris or rhizome iris (called rhizomatous) with a number of further subdivisions. Due to a wide variety of geographic origins, and thus great genetic diversity, cultivation needs of iris vary greatly.
Iris grow well in most any garden soil types providing they are well-drained. The earliest to bloom are species like I. junonia and I. reichenbachii, which flower as early as February and March in the Northern Hemisphere, followed by the dwarf forms of I. pumila, and then by most of the tall bearded varieties, such as the German iris and its variety florentina, sweet iris, Hungarian iris, lemon-yellow iris (I. flavescens), Iris sambucina, I. amoena, and their natural and horticultural hybrids such as those described under names like I. neglecta or I. squalens and best united under I. × lurida.
Bearded rhizome iris
Bearded iris are classified as dwarf, tall, or aril. In Europe, the most commonly found garden iris is a hybrid iris (falsely called German iris, I. germanica which is sterile) and its numerous cultivars. Various wild forms (including Iris aphylla) and naturally occurring hybrids of the Sweet iris (I. pallida) and the Hungarian iris (I. variegata) form the basis of almost all modern hybrid bearded irises. Median forms of bearded iris (intermediate bearded, or IB; miniature tall bearded, or MTB; etc.) are derived from crosses between tall and dwarf species like Iris pumila.
Bearded iris are easy to cultivate and propagate and have become very popular in gardens. A small selection is usually held by garden centres at appropriate times during the season, but there are thousands of cultivars available from specialist suppliers (more than 30 000 cultivars only for the tall bearded irises !). They are best planted as bare root plants in late summer, in a sunny open position with the rhizome visible on the surface of the soil and facing the sun. They should be divided in summer every two or three years, when the clumps become congested.
A truly red bearded iris, like a truly blue rose, remains an unattained goal despite frequent hybridizing and selection. There are species and selections, most notably based on the beardless rhizomatous Copper iris (I. fulva), which have a relatively pure red color. However, getting this color into a modern bearded iris breed has proven very difficult, and thus, the vast majority of irises are in the purple and blue range of the color spectrum, with yellow, pink, orange and white breeds also available.
Bearded iris Oncocyclus section
This section contains the cushion irises or royal irises, a group of plants noted for their large, strongly marked flowers. Between 30 and 60 species are classified in this section, depending on the authority. Compared with other irises the cushion varieties are scantily furnished with narrow sickle-shaped leaves and the flowers are usually borne singly on the stalks; they are often very dark and in some almost blackish. The cushion irises are somewhat fastidious growers, and to be successful with them they must be planted rather shallow in very gritty well-drained soil. They should not be disturbed in the autumn, and after the leaves have withered the roots should be protected from heavy rains until growth starts again naturally.
Bearded iris Regelia section
This section, closely allied to the cushion irises, includes several garden hybrids with species in section Oncocyclus, known as Regelio-cyclus irises. They are best planted in September or October in warm sunny positions, the rhizomes being lifted the following July after the leaves have withered.
Beardless rhizome iris (subgenus Limniris)
There are six major subgroupings of the beardless iris, depending on origin. They are divided into Pacific Coast, Siberica, Spuria, Louisiana, Japanese, and other.
Beardless rhizomatous iris types commonly found in the European garden are the Siberian iris (I. sibirica) and its hybrids, and the Japanese Iris (I. ensata) and its hybrids. "Japanese iris" is also a catch-all term for the Japanese iris proper (hanashōbu), the blood iris (I. sanguinea, ayame) and the rabbit-ear iris (I. laevigata, kakitsubata). I. unguicularis is a late-winter-flowering species from Algeria, with sky-blue flowers blotched with yellow, produced from Winter to Spring. Yet another beardless rhizomatous iris popular in gardening is I. ruthenica, which has much the same requirements and characteristics as the tall bearded irises. In North America, Louisiana iris and its hybrids are often cultivated.
Crested rhizome iris (subgenus Limniris)
One specific species, Iris cristata from North America.
Bulbing juno iris (subgenus Scorpiris)
Often called 'junos', this type of iris is one of the more popular bulb irises in cultivation. They are generally earliest to bloom.
Bulbing European iris (subgenus Xiphium)
This group includes irises generally of European descent, and are also classified as Dutch, English, or Spanish iris.
- Iris reticulata and Iris persica, both of which are fragrant, are also popular with florists.
- Iris xiphium, the Spanish Iris (also known as Dutch Iris) and
- Iris latifolia, the English Iris. Despite the common names both the Spanish and English iris are of Spanish origin, and have very showy flowers, so they are popular with gardeners and florists. They are among the hardier bulbous irises, and can be grown in northern Europe. They require to be planted in thoroughly drained beds in very light open soil, moderately enriched, and should have a rather sheltered position. Both these present a long series of beautiful varieties of the most diverse colours, flowering in May, June and July, the smaller Spanish iris being the earlier of the two.
Bulbing reticulate iris (subgenus Hermodactyloides)
Reticulate irises with their characteristic bulbs, including the yellow I. danfordiae, and the various blue-purple I. histrioides and I. reticulata, flower as early as February and March. These reticulate-bulbed irises are miniatures and popular spring bulbs, being one of the first to bloom in the garden. Many of the smaller species of bulbous iris, being liable to perish from excess of moisture, should have a well-drained bed of good but porous soil made up for them, in some sunny spot, and in winter should be protected by a covering of half-decayed leaves or fresh coco-fiber.
Iris atropurpurea, a dark flowered, bearded Oncocyclus iris
Rhizomes of the German Iris (I. germanica) and Sweet Iris (I. pallida) are traded as orris root and are used in perfume and medicine, though more common in ancient times than today. Today Iris essential oil (absolute) from flowers are sometimes used in aromatherapy as sedative medicines. The dried rhizomes are also given whole to babies to help in teething. Gin brands such as Bombay Sapphire and Magellan Gin use orris root and sometimes iris flowers for flavor and color.
For orris root production, iris rhizomes are harvested, dried, and aged for up to 5 years. In this time, the fats and oils inside the roots undergo degradation and oxidation, which produces many fragrant compounds that are valuable in perfumery. The scent is said to be similar to violets. The aged rhizomes are steam-distilled which produces a thick oily compound, known in the perfume industry as "iris butter" or orris oil.
Iris rhizomes also contain notable amounts of terpenes, and organic acids such as ascorbic acid, myristic acid, tridecylenic acid and undecylenic acid. Iris rhizomes can be toxic. Larger blue flag (I. versicolor) and other species often grown in gardens and widely hybridized contain elevated amounts of the toxic glycoside iridin. These rhizomes can cause nausea, vomiting, diarrhea, and/or skin irritation, but poisonings are not normally fatal. Irises should only be used medicinally under professional guidance.
In water purification, yellow iris (I. pseudacorus) is often used. The roots are usually planted in a substrate (e.g. lava-stone) in a reedbed-setup. The roots then improve water quality by consuming nutrient pollutants, such as from agricultural runoff. This highly aggressive grower is now considered a noxious weed and banned in some states of the US where it is found clogging natural waterways.
The Iris croatica is the unofficial National Flower of Croatia . Iris nigricans, the Black Iris is the national flower of Jordan. Iris bismarckiana, the Nazareth Iris, is the symbol of the city of Upper Nazareth.
An iris — species unspecified — is one of the state flowers of Tennessee. It is generally accepted that the species Iris versicolor, the Purple Iris is the state flower alongside the wild-growing purple passionflower (Passiflora incarnata), the state's other floral emblem. Greeneville, Tennessee, is home to the annual Iris Festival celebrating the iris, local customs, and culture. The species Iris versicolor is also the provincial flower of Quebec, having replaced the Madonna lily which is not native to the province. and it is the official flower of Kappa Pi International Honorary Art Fraternity.
The American artist Joseph Mason – a friend of John James Audubon – painted a precise image of what was then known as the Louisiana flag or copper iris (Iris fulva), to which Audubon subsequently added two Northern paraula birds (Parula americana) for inclusion as Plate 15 in his Birds of America.
The artist Philip Hermogenes Calderon painted an iris in his 1856 work Broken Vows; he followed the principles of the Pre-Raphaelite Brotherhood. An ancient belief is that the iris serves as a warning to be heeded, as it was named for the messenger of Olympus. It also conveys images of lost love and silent grief, for young girls were led into the afterlife by Iris. Broken Vows was accompanied with poetry by Henry Wadsworth Longfellow when it was first exhibited.
The fleur-de-lis, a stylized iris, first occurs in its modern use as the emblem of the House of Capet. The fleur-de-lis has been associated with France since Louis VII adopted it as a symbol in the 12th century. The yellow fleur-de-lis reflects the yellow iris (I. pseudacorus), common in Western Europe. Contemporary uses can be seen in the Quebec flag and the logo of the New Orleans Saints professional football team and on the flag of Saint Louis, Missouri.
The red fleur-de-lis in the coat-of-arms and flag of Florence, Italy, descends from the white iris which is native to Florence and which grew even in its city walls. This white iris displayed against a red background was the symbol of Florence until the Medici family reversed the colors to signal a change in political power, setting in motion a centuries-long and still on-going breeding program to hybridize a red iris.
A stylized yellow iris is the symbol of Brussels, since historically the important Saint Gaugericus Island was carpeted in them. The iris symbol is now the sole feature on the flag of the Brussels-Capital Region. The provincial flower of Québec (Canada) is the harlequin blueflag (I. versicolor), called iris versicolore in French.
It is thought in China, that Iris anguifuga has the ability to keep snakes from entering the garden. It grows all winter, keeping snakes out, but then goes dormant in the spring, allowing the snakes back into the garden. In the autumn, the iris re-appears and can stop the snakes again.
In the Homeric Hymn to Demeter, the goddess Persephone and her companion nymphs (the Oceanids along with Artemis and Athena) were gathering flowers such as rose, crocus, violet, iris (also called 'agallis' or ἀγαλλίς (in Greek script), lily, larkspur, and hyacinth in a springtime meadow before she was abducted by the god Hades.
Philip Hermogenes Calderon's Broken Vows with the iris at lower left
Early coat-of-arms of the House of Capet (France ancient)
Variant on Fransaskois flag
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|Wikimedia Commons has media related to Iris (Iridaceae).|
|Wikimedia Commons has media related to Iris cultivars by alphabet.|
- Joseph Mason's painting - Copper Iris Copper Iris / Louisiana Flag (Iris cuprea) from John James Audubon's Birds of America
- Flora of North America: Iris
- Flora of China: Iris
- Flora of Pakistan: Iris
- Flora of Nepal: Iris
- A web site devoted to Irises, by David Payne-Joyce; includes plates from Dykes (1913).
- The American Iris Society
- Historic Iris Preservation Society
- An extensive website about Iris
- Iris listings at Wild Flowers of Israel
- Iris in Art and Culture
- Gouvernement du Québec Emblèmes du Québec - Iris versicolor (French)