Illustration of an iris flower with highlighted parts of the flower
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.
inflorescences are in the shape of a fan and contain one or more symmetrical six-lobed
flowers. These grow on a
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 plants
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
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.
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