Iris (plant)
Iris is a flowering plant genus of 310 accepted species with showy flowers. 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, Hermodactylus, and Pardanthopsis 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.
Description
Irises are perennial plants, growing from creeping rhizomes or, in drier climates, from bulbs. 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 also have 2–10 narrow leaves growing from the bulb.Flower
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, into a broader expanded portion and can be adorned with veining, lines or dots. In the centre of the blade, some of the rhizomatous irises have a "beard", a row of fuzzy hairs at the base of each falls petal which gives pollinators a landing place and guides them to the nectar.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. The three 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 three 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.
The iris fruit is a capsule which opens up in three parts to reveal the numerous seeds within. In some species, the seeds bear an aril, such as Iris stolonifera which has light brown seeds with thick white aril.
Etymology
The genus takes its name from the Greek word ἶρις îris "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.Taxonomy
Iris is the largest genus of the family Iridaceae with up to 300 species – many of them natural hybrids. Plants of the World Online lists 310 accepted species from this genus as of 2022. Modern classifications, starting with Dykes, have subdivided them. Dykes referred to the major subgroupings as sections. Subsequent authors such as Lawrence and Rodionenko have generally called them subgenera, while essentially retaining Dykes' groupings, using six subgenera further divided into twelve sections. Of these, section Limneris was further divided into sixteen series. Like some older sources, Rodionenko moved some of the bulbous subgenera into separate genera, but this has not been accepted by later writers such as Mathew, 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 or absence of arils on the seeds, referred to as arilate or nonarilate. Taylor 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 has a Holarctic distribution. The two largest subgenera are further divided into sections. The Iris subgenus has been divided into six sections; bearded irises, Psammiris, Oncocyclus, Regelia, Hexapogon and Pseudoregelia. Iris subg. Limniris has been divided into 2 sections; Lophiris and Limniris which was further divided into 16 series.
Evolution
The concept of introgressive hybridization was first coined to describe the pattern of interspecific hybridization followed by backcrossing to the parentals that is common in this genus.Subgeneric division
Subgenera
- Iris
- Limniris
- Xiphium
- Nepalensis
- Scorpiris
- ''Hermodactyloides''
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, woodland, bogs and riverbanks. Some irises like Iris setosa can tolerate damp or dry sites, and Iris foetidissima can be found in woodland, hedge banks and scrub areas.Diseases
Narcissus mosaic virus is most commonly known from Narcissus. Wylie et al., 2014, made the first identification of Narcissus mosaic virus infecting this garden plant genus, and the first record in Australia. Japanese iris necrotic ring virus also, commonly infects this genus. It was, however, unknown in Australia until Wylie et al., 2012, identified it in Australia on I. ensata.Cultivation
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 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 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.
Generally, Irises grow well in most garden soil types providing they are well-drained, depending on the species. The earliest to bloom are species like I. reticulata and I. reichenbachii, which flower as early as February and March in the Northern Hemisphere, followed by the dwarf forms of I. pumila and others. In May or June, most of the tall bearded varieties start to bloom, such as the German iris and its variety florentina, sweet iris, Hungarian iris, lemon-yellow iris, Iris sambucina, and their natural and horticultural hybrids such as those described under names like I. neglecta or I. squalens and best united under I. × lurida.
The iris is promoted in the United Kingdom by the British Iris Society. The National Collection of Arthur Bliss Irises is held in Gloucestershire.
The American Iris Society is the International Cultivar Registration Authority for Iris, and recognises over 30,000 registered cultivar names.
Bearded rhizome iris
Bearded iris are classified as dwarf, tall, or aril. In Europe, the most commonly found garden iris is a hybrid iris and its numerous cultivars. Various wild forms and naturally occurring hybrids of the Sweet iris and the Hungarian iris form the basis of almost all modern hybrid bearded irises. Median forms of bearded iris are derived from crosses between tall and dwarf species like Iris pumila.The "beard", short hairs arranged to look like a long furry caterpillar, is found toward the back of the lower petals and its purpose is to guide pollinating insects toward the reproductive parts of the plant. Bearded irises have been cultivated to have much larger blooms than historically; the flowers are now twice the size of those a hundred years ago. Ruffles were introduced in the 1960s to help stabilize the larger petals.
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. 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, 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. Irises like many related genera lack red-based hues because their anthocyanins are delphinidin-derived. Pelargonidin-derived anthocyanins would lend the sought-after blue-based colors but these genera are metabolically disinclined to produce pelargonidin. Dihydroflavonol 4-reductases in Iriss relatives selectively do not catalyse dihydrokaempferol to leucopelargonidin, the precursor, and this is probably the case here as well. The other metabolic difficulty is the presence of flavonoid 3'-hydroxylase, which in Chrysanthemum inhibits pelargonidin synthesis. The bias in irises towards delphinidin-anthocyanins is so pronounced that they have served as the gene donors for transgenic attempts at the aforementioned blue roses. Although these have been technically successful over 99% of their anthocyanins are blue their growth is crippled and they have never been commercializable.