Irises are perennial herbs, grown from creeping rhizomes(rhizomatous irises), or, in dry climates, from bulbs(bulbous irises). They have longer, erect flowering stems, which could be simple or branched, solid or hollow, and flattened or have a circular cross-section. The rhizomatous species may have 3–10 basal, sword-shaped leaves growing in dense clumps. The bulbous species have cylindrical, basal leaves.

The inflorescences are fan-shaped and contain one or more symmetrical six-lobed flowers. These bloom on a pedicel or lack a footstalk. The three sepals, which are spreading or droop downwards, are called "falls". They expand from their narrow base, which in some of the rhizomatous irises has a "beard", into a broader expanding portion , often adorned with veining, lines or dots. The three, sometimes reduced, petals stand upright, partly behind the sepal bases. They’re called "standards". Some smaller iris species have all six lobes pointing straight out, but generally, limb and standards differ markedly in appearance. They are united at their base into a floral tube that lays above the ovary(known as an inferior ovary). The styles separate towards the apex into petaloid branches; this is significant in pollination.