Iris is a genus of flowering plants with showy flowers ranging in color from gold, copper-red or yellow to white, blue, blue-violet, lavender, tan, maroon and purple.
Pink and apricot colored irises have also been bred in some species. The name “Iris” can be applied to the genus or to any of the species within it. It is also applied to various subdivisions within the genus.
There are many species of iris widely distributed throughout the northern temperate zone. Their habitats are very varied and range from cold regions into the grassy slopes, meadowlands, stream banks and deserts of Europe, the Middle East and northern Africa, Asia and southern North America. Elevation is of little importance.
These perennial herbs grow from creeping rhizomes (rhizomatous irises), or, in drier climates, from bulbs (bulbous irises). They have long, erect, flowering stems and may be simple or branched, solid or hollow. The stalks may be flattened or have a circular transverse section. There are 3 – 10 basal, sword-shaped leaves growing in dense clumps.
The flower heads are fan-shaped and contain 1 or more symmetrical, six-lobed, slightly fragrant flowers. These grow on a pedicel or lack a footstalk. The three sepals are spreading are sagging downwards. They expand from their narrow base into a broader limb (= expanded portion), adorned with lines or dots. The three, sometimes reduced, petals stand upright, partly behind the sepal bases. Some smaller iris species have all six lobes pointing straight outwards. The sepals and the petals differ from each other. They are united at their base into a floral tube that lies above the ovary. The styles divide towards the apex into petaloid branches.
The flag irises are for the most part of the easiest culture and easily propagated. They have become very popular in the garden. They grow in any good free garden soil, the smaller and more delicate species only needing the aid of turfy ingredients, either peat or loam, to keep it light and open in texture. The earliest to bloom are the dwarf forms of Iris pumila, which blossom during March, April and May; and during the latter month and the following one most of the larger growing species, such as I. germanica, fiorenhina, pallida, variegata, amoena, flavescens, sambucina, neglecta, ruthenica, etc., produce their flowers. Of many of the foregoing there are, besides the typical form, a considerable number of named garden varieties. Iris unguicularis (or stylosa) is a remarkable winter flowering species from Algeria, with sky-blue flowers blotched with yellow, produced (in the Northern Hemisphere) at irregular intervals from November to March, the bleakest period of the year.
Many other 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 6-in, covering of half-decayed leaves or fresh coco-fiber refuse. To this set belong milifolia, junonia, danfordiae, reichenbachii and others which flower as early as February and March.
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.
The iris flower is of special 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 the perianth for honey will first come in contact of perianth, three with the stigmatic stamens in one whorl surface which is borne and an ovary formed of three carpels. The shelf-like transverse projection on the inner whorl under side of the stamens, which is beneath the over-arching style arm below the stigma, so that the insect comes in contact with its pollen-covered surface only after passing the stigma, while in backing out of the flower it will come in contact only with the non-receptive lower face of the stigma. Thus a insect bearing pollen from one flower will in entering a second deposit the pollen on the stigma, while in backing out of a flower the pollen which it bears will not be rubbed off on the stigma of the same flower.
Up to 300 species have been placed in the genus Iris. Modern classifications, starting with W. R. Dykes’ 1913 book, have subdivided them. Dykes referred to the major subgroupings as sections, but later authors have generally called them subgenera, while essentially retaining his groupings. Like some older sources, the influential classification by G. I. Rodionenko removed some groups (particularly the bulbous irises) to separate genera, but even if this is done the genus remains large and several subgenera, sections and/or subsections are recognized within it.