There are roughly 200 species of the iris flower throughout the world, the most popular being the bearded or German Iris with the next most popular type being the Siberian Iris. Broadly speaking, the iris has two major classifications, rhizome and bulbous, which have to do with the base of the plant and its root system, according to The Flower Expert. There are many varieties of irises within those two categories.
Rhizome irises generate sword-shaped leaves that overlap to form green, fan-shaped mats of foliage. Bearded, beardless and crested irises all fall within this category. As their names imply, bulbous irises grow from bulbs and require periods of dormancy after they initially bloom. The bulbous varieties are generally smaller than rhizome irises and produce smaller flowers. The Flower Expert reports that the purple iris, the Tennessee state flower, is a bearded iris, making it part of the rhizome category.
Irises grow in varied climates and terrains throughout the world, according to American Meadows. The flower is found in swamps, deserts, temperate climates and cold regions in both hemispheres and on all continents.
Japanese irises, which bloom in late summer, are another popular type. Louisiana irises, which grow in or near wetlands, come in a wide variety of colors and styles.