Papaver somniferum, better know as the opium poppy, is a Eurasian native, widely cultivated for the sticky gum produced by maturing seed pods, which is the source of opium, morphine and codeine. Its nutritious seeds, which contain no narcotic substances, are used for baking. The opium poppy has naturalized over much of the United States, and can sometimes be found growing along roadsides. This showy annual bears large, papery flowers in white, red and shades of lavender. There are several varieties of Papaver somniferum, some of which superficially resemble their cultivated and wild relatives. When they're in bloom, you can identify them by a few distinguishing characteristics.
Observe the color patterns, shape and number of the petals. P. somniferum varieties have large flowers with up to eight petals, whereas other species will only have four to five. P. somniferum giganteum has vivid red or white petals with a characteristic dark spot at the base. The "Persian White" variety has pure white petals throughout. "Danish Flag" sports a very showy combination of white and red, and is hard to confuse with other poppies because of its color and pattern. The lilac-flowered varieties of this subspecies are quite distinctive because of their color, which sets them apart from other cultivated poppies. Unlike other poppies, P. somniferum paeoniflorum features highly double, fringed petals, which resemble peonies or pom-poms. (See Reference 1)
Examine the growth habit and height of the flower stalks. P. somniferum grows from three to five feet tall, which is much taller than most other cultivated and native poppies. The green, toothed leaves, which can measure up to six inches across, are also considerably larger than those of other kinds of poppies.
Study the seed pods once the petals have fallen away. P. somniferum pods are an inch to an inch-and-a-half in diameter and quite globe-shaped, while most poppies native to the U.S. have much smaller, elongated pods. Look for a pronounced, multi-pointed star shape at the top of the round, smooth seed pod. (See Reference 1)
Shake the seeds out of the dry pods and inspect them. P. somniferum's small seeds are commonly slate blue or light tan. The blue ones are the familiar seeds used in baking.