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Prickly poppies are distinguished from other species in the genus Argemone by the lack of spines on the upper sides of leaves

Prickly poppies, Argemone polyanthemos, were abundant and in full bloom along the Degge Trail in the greenbelt north Boulder. I enjoyed examining the blooms to see the pollinating solitary bees, flies, beetles and butterflies, and watched a scarab beetle known as the common flower beetle, Euphoria kernii, trundling through a forest of stamens, gulping pollen.

At the top of the page: A pair prickly poppies. Above: A prickly poppy. Photos by Jeff Mitton.

The genus Argemone is composed of about 30 species native to North America and the West Indies, plus one endemic to Hawaii. A. polyanthemos is native to the sandy soils of the Great Plains from Texas and New Mexico to South Dakota. Following its adoption as an ornamental, it has expanded its range to areas west of the Rocky Mountains. 

Prickly poppies are annuals or biennials that thrust taproots deep into the ground for water and grow three to five feet tall. They produce flowers all summer. Each flower is three to four inches wide with four to six crumpled, white petals. Its numerous stamens are bright yellow, encircling a style tipped by a three to five lobed, reddish brown to red stigma. Leaves are deeply lobed, about eight inches long, and leaves, stems and seed pods are light bluish green. 

Prickly poppies, as the common name suggests, are defended by sharp, stiff spines radiating from seed pods, buds, stems and leaf margins. Prickly poppies are distinguished from other species in the genus Argemone by the lack of spines on the upper sides of leaves. One might suppose that numerous spines capable of piercing flesh would be an adequate defense, but for prickly poppies, spines are only the first defense. Remember that while some herbivores are large and challenged by spines, small insect herbivores walk among the spines with impunity. 

When a stem or leaf is broken, a yellowish orange mixture of latex and sap exudes from the rupture. Latex, produced by about 10% of angiosperms and all Argemone species, is an emulsion of proteins, alkaloids, gums, oils and resins that that coagulates when exposed to air. Latex constitutes a defense system by itself, for its sticky, rubbery, mucilaginous consistency is not pleasant to any palate, it can be difficult to remove and it can bind tiny insect mouth parts together. But in addition, latex may contain defensive chemicals in concentrations ten to 100 times those in other plant fluids or tissues. 

A scarab beetle harvests pollen from a prickly poppy. Photo by Jeff Mitton.

Plant biologists had determined that species of Argemone were defended by alkaloids, and in 1974 a paper announced that a new long chain alkaloid, argemonic acid, had been described in Mexican prickly poppy and was later confirmed to defend other species of Argemone. At that time, argemone oils were used to season food in India, and argemonic acid was implicated in an epidemic of dropsy. This development inspired further studies of compounds in A. mexicana with biological activity that would provide chemical defenses. These studies yielded a set of nineteen defensive chemicals, including the alkaloids berberine, chelerythrine, sanguinarine and pancorine--a veritable pharmacy. The biological activities of the chemical defenses include antibacterial, anti-HIV, wound healing, anti-stress, antiallergic, anti-fertility, cytotoxic, nematicidal, fungitoxic, larvicidal, antioxidant and anticancer. This bouquet of defensive compounds imparts an acrid taste to leaves and stems, which is sufficient to immediately deter most herbivores. 

Long before Europeans discovered the West Indies and North America, Native Americans were aware of the biological activities of extractions from poppies and using Argemone as source of medicines. Shoshone, Paiute, Tepehuan, Comanche, Hopi and Aztec peoples used concoctions derived from poppies for anesthetizing fish, sedating humans, removing warts, treating cold sores, cuts, scrapes and congestion associated with colds and flu, and as a soporific, an emetic and a laxative. The first Americans had other uses for poppies as well, including dies for fabrics and for tattoos. 

Efficacy of prickly poppy defenses is apparent when a variety of plants are exposed to high herbivore pressure, and cattle and sheep ranchers have unwittingly conducted this experiment countless times. A most robust outcome of this experiment is that as other plant species dwindle and disappear, abundance of prickly poppies increases, so that we recognize prickly poppies as an indicator of an overgrazed landscape. Prickly poppy's large flowers and abundant pollen attract many pollinators, but spines and an elaborate defensive pharmacy protect leaves, stems and seed pods from herbivores.