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U.S. Forest Service

The Iris Flower

The competition for pollinators is intense evolving in a habitat where numerous other species of flowering plants are blooming at the same time. Irises have developed a highly specialized flower. The blossoms are very large and colorful.

blue flag iris flower. The parts of the flower are labeled. Figure 1. The parts of an iris flower. Image by Jim Conrad, Backyard Nature.

In Figure 1, the sepals (sometimes called “falls”) are recurved in such a manner to provide a landing pad for bumblebees. The petals (sometimes called “standards”) are upright and colorful, adding to the overall attractiveness of the flower to bumblebees. The striking and colorful veining on the sepals directs bumblebees down into a tight space between the sepal and style arm.

Close-up the style arm of an iris flower. The parts are labeled. Figure 2. The iris style arm. Image by Jim Conrad, Backyard Nature.

The style arm (Figure 2) is a highly modified pistil that connects the stigmatic lip to the ovary. While crawling down toward the nectar glands, pollen rubs off the back of the pollinator and attaches to the sticky stigmatic lip. Moving ever forward, the bumblebees’ backs come in contact with the pollen-producing anthers on the stamen where they pick up additional pollen. Botanists believe that this relatively large and colorful modified pistil adds to the overall attractiveness of the blossom to bumblebees.

Blue Flag Irises…