Common Milkweed (Asclepias syriaca)
The eastern two-thirds of South Dakota is home to common milkweed. Elsewhere, the species ranges from Maine to Manitoba, south to Georgia and Texas.
Like many of our milkweeds, common milkweed is perennial from a deeply buried rhizome. The stout stems are usually solitary, covered with short, fine hairs, and, when severed, exude copious amounts of milky latex. Plants can be up to six feet tall, but South Dakota specimens are usually only about half that height. The opposite leaves are up to 4 inches wide and 8 inches long and covered with fine white hairs, especially below. From one to three inflorescences, each bearing 20 to 100 or more rose- to purplish-white flowers are borne on stalks (peduncles) that arise from the upper leaf axils. At maturity, the specialized fruits, termed follicles by botanists, are up to four inches long and 1-1/2 inches thick. Inside these usually warted, pod-like structures are large seeds bearing white hairs nearly two inches long.
Look for common milkweed from June through August on native prairie, roadsides, and most other open habitats that are not heavily grazed by livestock. Domestic livestock has been poisoned by milkweeds, but all milkweeds are distasteful to livestock, and losses occur only when animals are forced to eat these plants. Common milkweed has a long history of use as human food. The young shoots and well-filled follicles of this plant are edible if boiled with one or two changes of water. These were a staple of many Amerindian tribes and thought to be cultivated by some. The dried latex was chewed. The roots were used for various diseases of the lungs and thorax and were listed in the U. S. Pharmacopeia in the late 1800s. The follicles were also gathered during World War II for their fluffy seeds that substituted for kapok in emergency flotation devices.
Most of the roughly 2,400 species in the milkweed family (Asclepiadaceae after Asklepios, the Greek god of medicine) are found in Africa and tropical America. Most of the roughly 100 species in the genus Asclepias are found in America. The Swedish father of modern plant taxomony, Carl von Linne (Linneaeus) described common milkweed for science in the mid-1700s. He erroneously assigned the plant the specific epithet syriaca because he thought that the type specimens had been carried to Europe from the Orient, rather than from eastern North America. But we are stuck with this misnomer, because in botany, a name first used to describe a valid species is unchangeable, regardless of errors in derivation or spelling.
TOXICITY RATING: Low to moderate. Milkweeds are unpalatable, and have variable toxicities. Death is not likely unless large quantities are consumed.
ANIMALS AFFECTED: All animals may be affected. Sheep are most at risk, but cattle, goats, horses, poultry, and pets are also at risk.
DANGEROUS PARTS OF PLANT: Stems, leaves, roots.
CLASS OF SIGNS: Gastrointestinal irritation (primarily vomiting and diarrhea), incoordination, tremors, heart problems, respiratory difficulty, death.
PLANT DESCRIPTION: Milkweeds, such as common milkweed, Asclepias syriaca (fig. 26), get their name from the thick, sticky, milky sap that oozes out of cut or torn leaves, stems, and fresh pods. The usually solitary stems of milkweed grow 1 to 5 feet tall and bear opposite (sometimes whorled), sometimes fleshy leaves with entire margins. Flowers emerge in umbrella-like clusters and range in color from pink to rose-purple to orange or white. The fruit (fig. 26A) is a pod with "tufted" seeds. A dozen species of milkweeds grow in Indiana woods and swamps, but most commonly in dry soils of fields and road- sides. Dogbanes (Apocynum spp.), which are easily confused with milkweeds, are found in the same habitats and may causesimilar poisoning.
SIGNS: There are several different types of milkweeds with varying degrees of toxicity, with the whorled milkweeds being the most toxic. Milkweed plants are considered unpalatable and are eaten only when other forages are not available, and may also be found in hay and processed feeds. The primary toxicants are cardiac glycosides that cause gastrointestinal, cardiac and respiratory problems and can cause death if enough is consumed. Resins (especially galitoxin) in the milky sap may also contribute to the toxicity of milkweed. In ruminants, the first signs are incoordination, muscle tremors and spasms, bloat, increased heart rate, breathing problems, and occasionally death. Horses are very reluctant to eat this plant, and its toxicity is only rarely reported: colic, diarrhea, abnormal heart rate and rhythm, rarely death. In animals that are capable of vomiting (pigs, dogs, cats, humans), this is the first sign to develop and is beneficial in that further absorption of the toxin is lessened. Horses cannot vomit, and vomiting is not generally observable in ruminants (if vomiting occurs, the contents still remain in the rumen), therefore toxic signs will be worse in these species.
FIRST AID: There is no antidote if an animal consumes milkweed. It is important to limit further ingestion of the plants or contaminated feed. If the animal recently consumed a large amount of the plant, a veterinarian should be called so that the gastrointestinal tract can be emptied and supportive care provided. Small tastes of the plants tend to result in minor oral irritation, and serve as a deterrent to further consumption, and these little nibbles typically do not require treatment.
SAFETY IN PREPARED FEEDS: Milkweed is toxic both fresh and dried, therefore hay, silage, green chop, and processed feeds that contain milkweed are never safe for consumption.
PREVENTION: Animals will avoid milkweed as long as there is sufficient forage available. Care must be taken to avoidincorporation of milkweed into prepared feeds and hay, and these feeds should be discarded.