Common Milkweed is a stout erect perennial, from 3 to 6 feet high. The stems are hairy, unbranched, and usually solitary. Like other milkweeds, the stem has a milky sap and is toxic.
Leaves are medium green, opposite and ovate with hairy undersides and a prominent center vein that is a yellowish color. They taper to a sharply pointed tip, have a tapered base with a short stalk, and have entire margins.
The inflorescence consists of stalked drooping umbels, dense with small stalked flowers, that rise from the upper leaf axils.
The flowers are 5-parted and when open, have five erect hood-like nectaries with the petal parts bent downward. The hoods each have a small horn on the inner side that curves inward and on this species, is shorter than the hood. The "common" milkweed has rose-purplish-greenish hoods and petals, the hoods usually lighter in color. Eloise Butler explains the function of these parts in her notes below.
The pollination system of Milkweeds works like this: The pollen of the milkweed is not in the form of free grains attached to an anther, but is contained in a waxy sac called a "pollinium" [plural - pollinia] with each sac having about a few hundred grains. Each Milkweed flower has two ovaries connected to the five flower parts, each part has a very short pistil with an enlarged stigma which has the form of a deep slit. Pollina sacs are in pairs with one sac located on each side of the stigma and each of the pair of sacs is connected by a 'translator arm' to a structure called a 'corpusculum' which sits atop the stigma slit. There is a groove in the corpusculum and the foot of an insect, such as a bee or butterfly, gets caught in the groove and when the foot is pulled out, the pair of sacs and the associated structure comes along with the foot and thus are then carried from flower to flower by the insects resulting in pollination. Any insect large enough and strong enough to remove the sac can fertilize another plant.
The method of fertilization is also interesting. Once a corpusculum has been pulled out, after a few minutes, the translator arms rotate the pulled out sacs 90 degrees. After the rotation when the insect reaches another flower, the sac is now in position to fit into the bottom of the slit in the stigma. As the insect moves its foot the sac is pulled upward in the slit until it hits the still existing corpusculum of that flower. At that point the translator arm snaps off and the pollen sac is in position to fertilize the flower. When the corpusculum of that flower is still present it is possible for the insects foot to catch it and thus remove another pair of pollen sacs for another go at the next flower. When the corpusculum of a flower has already been removed the chances of the translator arm breaking off are reduced and the pollina sac may not be broken off and is carried away by the insect to another plant.
Thus those flowers with their corpusculum still in place have the greatest chance of being fertilized. This is why the numerous flowers result in only a few seed pods. The fact that the translator arms take a few minutes to rotate after being pulled from a flower prevents the insect from cross pollinating adjacent flowers and allows the insect to find other plants that may not be clones of the first plant the insect visited. [This summary is based on the research work of Douglass H. Morse of Brown University.]
Seeds: The seeds form in long pods (a follicle) that are erect on stalks that are downward pointing. The mature seed pod has a warty appearance and contains a large number of flat brown seeds attached to long white silky hairs. When the pod splits, these are dispersed by wind. Notes within the photo section detail the mechanism of dispersion. Seeds require 30 days of cold stratification for germination.
Habitat: Common Milkweed spreads by rhizomes and by the seeds. As the rhizome sends out underground shoots, it can tend to be invasive if allowed - see notes at page bottom about the problems in Europe with the species. The plants formed from the rhizome are all clones. The plant requires partial to full sun and tolerates dry to wet, but well drained, locations. It is a common plant of our roadsides and waste places and open fields. Common Milkweed is readily propagated by cuttings of the rhizome, done when the plant is dormant. Each cutting should have one bud. This should be done so that the plants are in the ground by late fall and then can develop roots to survive the winter. Seed propagation is also very effective in the fall. Seedlings and cuttings will bloom the second year. Kansas State University has developed a hybrid that could grow as a crop as the plant is easily cultivated. (Ref #14).
Names: The Angiosperm Phylogeny Group in 2000 re-assigned the Ascelepias genus to the Apocynaceae family from the previous Asclepiadaceae (Milkweed) family. You will find many references that have not yet picked this up. The genus name Asclepias is named for the Greek god of healing "Asklepios" and syriaca is "of Syria." The author name for the plant classification, 'L.', refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. For more info and lore see below.
Comparisons: The showy drooping pinkish dense umbels of flowers rising from the leaf axils at the top of the plant which is unbranched, will help identify this species of milkweed. See in 'notes' below links to other species.
Above: The inflorescence consists of stalked drooping umbels, dense with small stalked flowers, that rise from the upper leaf axils.
Below: Flower detail showing the five erect hoods with the petal parts bent downward and the small horns leaning inward, typical of Milkweeds.
Below - Plant Development: Some young plants do not produce the large umbel containing many flowers. Flower structures are green prior to the the petals reflexing.
Above and Below: Note in the 3rd photo above and the 1st photo below the delicate arrangement of the seeds within the pod. All seeds are tucked around the central core of the pod with their silky parachutes upward and are attached to the central core of the pod which they hang from as the wind unfurls them and then (2nd photo below) - away they go, leaving an empty pod which has a very nice yellow color on the inside.
Below: Another ingenuous design inside the pod of milkweeds is a thin membrane attached at top and bottom of the pod. The white downy filaments of each seed are tucked into shallow crevices in this membrane allowing each seed to pull free from the pod individually, as it is ready, when the pod splits open.
Thoreau wrote in his journals: "I am interested in the fate or success of every such venture which the autumn sends forth. And for this end these silken streamers have been perfecting themselves all summer, snugly packed in this light chest, as perfect adaptations to this end - a prophecy not only of the fall, but of future springs."
Below: The milky latex contained in the stem.
Eloise Butler wrote: "Every one knows the tall, rank, Common Milkweed and probably admires more than the large umbels of pale purplish flowers the rough, gray seed pods, that, splitting down one side, disclose a wondrous freight of closely packed, brown seeds. A gust of wind quickly twirls these out; for each seed, in place of a magic carpet is provided with a tuft of white, silky down to transport it to some distant place." Published July 9, 1911, Minneapolis Sunday Tribune
Robert Frost wrote a poem about milkweed and Monarch Butterflies. Read it here: "Pod of the Milkweed"
Notes: Common Milkweed is indigenous to the Garden area. Eloise Butler catalogued it on May 31, 1907. Generally the plant is native throughout Minnesota and found in most counties except some scattered northern counties and the far NE Arrowhead. In North America, this plant is found from the East Coast west through the central plains.
There are 14 species of Milkweed native to Minnesota. Five of these are found in the Garden: A. exaltata, Poke Milkweed; A. incarnata, Swamp Milkweed; A. syrica, Common Milkweed; A. tuberosa, Butterfly Weed; and A. verticillata, Whorled Milkweed.
Eloise Butler wrote this about Milkweeds: "Most of the milkweeds, as the term implies, are furnished with a copious, milky juice. Crawling insects are likely to be covered and impaled by this sticky fluid, which exudes from wounds made by their sharp claws, as they scale the stems of the plants, and thus prevents them from rifling the nectar provided by the flowers for the pollen-distributing, hairy-bodied flying insects. Wonderful are the adaptations of the flower to desirable insect guests. Above the petals is a crown of five hood-like nectaries, each bearing within a slender, inverted horn. The center of the flower is designedly slippery. When an insect alights on this slimy surface to sip the abundant nectar, her feet slip and are tightly caught in crevices, also of fell design. When she extricates her toes, so to speak, she drags out attached to them a dangling pair of pollen masses - pollinia, a part of which is sure to adhere to the pistil of the next milkweed flower she visits. Insects have been caught at this season with stalks of these pollinia attached to every one of their six feet." Published in the Minneapolis Sunday Tribune July 9, 1911
The milky sap is toxic as are most other parts of the plant. Cattle and Sheep are particularly affected, rarely horses, and humans will find the young shoots and buds toxic in large quantities if not properly prepared. Toxins include the cardiac glycosides asclepiadin and asclepione, resinoids and a few alkaloids. The milky sap of the plant protects it from ants. Ants feet puncture the stem and they stick in the sap.
Edibility: However, with proper preparation, parts of the plant are edible. Proper cooking requires four minutes of boiling with at least one change of water to remove the toxins. Young shoots can be cooked as an asparagus substitute. Flowers, buds and immature fruit can be cooked. This was done by the Omaha and the Pawnee. The Sioux of the upper Platte ate the young pods, boiling them with buffalo meat, (as did the Crow and Cheyenne). This was reported on Pg. 16 of Fremont’s report to Congress on his 1842-43 Journey to the Rocky Mountains (Journal date June 22, 1842). Young sprouts can be confused with Prairie Dogbane (Apocynum cannabinum) which is more toxic than Common Milkweed. It comes up at the same time and also has milky sap. Dogbane stems however are smooth, tough, somewhat reddish and soon fork, whereas milkweed is usually unbranched.
Also mentioned by Fremont was the 'sugar report', of which many others have made similar notes, of making a sugar from the dew covered flowers. One other such report was by the Swedish traveler Pehr Kalm who wrote in the 18th Century that the French in Canada did this also. It remains unknown who learned from who. Kalm gave the procedure, which was to gather the flowers in the early morning when still dew covered. Press out the dew and boil the resulting liquid. This yields a very good brown palatable sugar. (Ref 6.)
Young seed pods while very immature and green make a palatable vegetable similar to Okra. This works until the pods become elastic to the touch - then they are tough and stringy. (Ref 6)
Medicinal: Using the root of the plant to produce a decoction taken by nursing women to produce a flow of milk, is commonly reported. Densmore (Ref. #5), in her study of the White Earth Chippewa, specifically lists this use. The prescription was to take 1/2 of a root, put it in a pint of boiling water and let it stand until cold. Then, whenever the woman took liquid food, to put a spoonful of this decoction in with it. (Ref. 5).
Modern herbalists only use roots of milkweed as a respiratory expectorant. In older times there was a long list of benefits; everything from poison ivy treatment to heart problem treatment. In the 1880s, the plant was adopted by the Canadian Pharmaceutical industry as an antiseptic. (Ref.# 39).
Other Uses: Other uses for the sap have been as a chewing gum when dried overnight by a fire. The bitter taste disappears some thereafter. The milky sap was looked to as a substitute for latex, which process proved impractical during W.W.II.
Dried Milkweed stalk has been used for fiber for making cords and ropes. Densmore (Ref. 5) also reports that the Chippewa created a charm by using root fibers, combined with root fibers of Boneset and then applying it to whistles for calling deer.
The Monarch Butterfly: Most people know the Monarchs are specific to milkweed plants. The cardiac glycoside in the sap makes a chemical defense for the Monarch caterpillar by making its flesh distasteful to most predators. Eggs are laid on the underside of healthy leaves, which the larvae will feed on before maturing into a chrysalis. All the Monarch, Queen and Viceroy butterflies have evolved into this pattern.
Invasive characteristics: While Common Milkweed can be somewhat invasive in North America, it has turned the tables on Europe where most of our invasive plants have come from. In Hungary at the Kiskunsag National Park, it has become so overwhelming that biologists are attempting, with some prospects of success, to train young rabbits (which also overrun the place) to eat the plant. They do this by trying to incorporate the plant into the diet of the female rabbits and then when young are raised, it has been noticed that the kittens will have an affinity for the food the mother ate. Thanks to The Economist of Aug. 20, 2016 for this little bit.
Saving the Milkweed in the Corn Belt: It is a common agricultural practice to eliminate milkweed in row crops and their adjacent borders by the application of herbicide. The most common pest of the Corn crop is the European Corn Borer and applications of pesticide are applied for this pest. Researchers have recently determined that the presence of Common Milkweed is a deterrent to the Corn Borer. It works like this: The milkweed attracts aphids which secrete honeydew. Wasps like honeydew and also corn borer eggs, so when the wasps are attracted to the milkweed for the honeydew they also find the corn borer eggs. What is not known is what ratio of milkweed plants left to mature to the size of the corn crop would provide good results. [From an article published in Weed Science in 2016 and reported in Kelseya, Winter 2017]
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"