Iris blossoms are highly specialized and different from our Standard Blossom in several interesting ways. The image at the right shows a typical iris flower with some of its unusual modifications.
The showy parts of iris flowers are not clearly distinguishable between calyx and corolla, as in our Standard Blossom. The lowest parts, where you'd expect the calyx to be, are just as colorful and fleshy as the upper parts, where the corolla should be.
IDENTIFICATION KEYS IN
FLORA OF NORTH AMERICA
You can "key out" your unknown finds of native plants belonging to the Iris Family at the Flora of North America website. Go to the key near the center of the page you arrive at when you click the above link, figure out your unknown plant's genus, click on the genus, then key out the species. These are technical keys using technical terms, but they are very useful.
When you want to refer to both calyx and corolla, or the showy parts where the calyx and corolla should be, you can call the whole structure a perianth. One specialized "perianth segment" of the iris blossom, situated where we'd expect a calyx's sepals to be, is the petal-like falls. The falls serves as a "landing pad" for pollinators. Notice how the falls in the flower above has bright lines leading into the blossom's mouth. These serve as nectar guides, directing pollinators toward the nectar.
The 3 standards correspond to a normal flower's petals. They rise above the blossom and provide more color and pollinator-attracting power to the flower.
The style arms are possibly the most surprising part of the blossom. In the Standard Blossom the style is the part of the female pistil that connects the ovary with the pollen-receiving stigma. Therefore, though style arms look like corolla petals, they are actually part of the blossom's female sex organ. One proof of that is that toward the top of the style arm you find the stigmatic lip, which actually serves as the stigma. When a pollinator enters the iris flower, it must squeeze beneath the stigmatic lip, and during this process pollen is scraped from the pollinator's body onto the stigmatic lip. There the pollen grains germinate and send down their pollen tubes carrying the male sex germ to ovules in the ovary.
The above picture shows how the style arm arches over the male stamen. The image at the right shows a detached style arm with its stamen.
One last interesting feature of iris blossoms is that in many species and varieties the upper surface of the falls is equipped with a beard consisting of fuzz such as that shown in the much-magnified image at the left. The beard gives pollinators something to hold on to as they enter the iris blossom in search of nectar.