The iris is a plant with long, sword-like leaves. Its flowers have six petals that form a tongue and "flags." When you cut through the stem to cut flowers for a bouquet arrangement, the many vascular bundles form tough "strings" throughout the stem. From this description, it is obvious that the iris is a

Iris is a genus of rhizomatous plants in the Iridaceae family.

Explanation:

Members of this genus are perennial herbaceous plants that grow from creeping rhizomes (rhizomatous irises) or, in drier climates, from bulbs (bulbous irises). They have long and erect flower stems, which can be simple or branched, solid or hollow and flattened or with circular cross sections.