Iris flowers are a common sight in gardens across the United States. The genus Iris contains more than 200 species of long-lived perennial flowers in many colors, shapes and sizes, all of which are adaptable to a wide range of growing conditions. The four principal types of iris flowers include bearded, beardless, crested and bulbous. Each type has distinct physical characteristics that differentiate it from the other types.

Bearded Iris

Bearded iris flowers are characterized by their bearded petals and are the easiest type to grow. They have three petals that stand upright, also known as standards. The three petals that hang down below the standards are known as falls. Each fall has a fuzzy strip or "beard" that runs along its length. Bearded irises are sometimes called German irises or pogoniris and produce flowers in a variety of colors including white, yellow, pink, purple, blue and multicolor. Thousands of bearded iris cultivars exist. Most bloom in spring, although some types can produce flowers in summer and fall. The American Iris Society classifies bearded irises into several types including miniature dwarf, standard dwarf, intermediate, miniature tall, border and tall. The smallest types may reach only 8 inches in height, while larger varieties can grow as tall as 38 inches. Bearded iris leaves are long, sword-shaped and evergreen in warmer climates. They will remain green until late fall in colder climates. The plants will tolerate droughts and cold temperatures, making them ideal for the beginning gardener.

Beardless Iris

Beardless iris flowers are similar in appearance to their bearded cousins, but they have smooth fall petals and thinner, more grass-like leaves. They are also known as apogoniris or apogons, and produce flowers in numerous colors including white, yellow, pink, purple, blue and maroon. Siberian, Japanese, Spuria, Louisiana and Pacific Coast Native are the most commonly grown beardless iris cultivars. They can grow from 1 to 5 feet tall, depending on the variety, and most types bloom in mid-summer after the bearded irises. Beardless irises love moist soil, making them ideal for planting around water gardens or near streams and ponds. They are grown from thick, fleshy rhizomes, or underground stems, which increase their tolerance of a wide range of soil conditions, including damp and even wet areas. They are not as susceptible to common iris flower pests and diseases such as bacterial soft rot or iris borer and can even bloom in partial shade.

Crested Iris

Crested iris flowers have a raised serrated ridge, or crest, running along the length of their falls in the same place the beard is located on bearded varieties. The color of the crest typically contrasts with the petal color. Crested irises are also grown from rhizomes and are closely related to bearded irises. However, they can generally tolerate more shade than the bearded types. One of the most commonly grown types of crested iris is Iris cristata, which is a dwarf variety native to America and features lavender flowers with yellow crests.

Bulbous Iris

Bulbous iris flowers differ from the other types because they are grown from bulbs instead of rhizomes. They are planted in fall and enter dormancy in the summer, during which time the bulbs may be lifted from the ground and stored until time to replant. Bulbous iris flowers are small, dainty and have even been called orchid-like. The most commonly grown types include English iris, Dutch iris and Spanish iris.