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Asclepias syriaca

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Asclepias syriaca

Secure  (NatureServe)
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Gentianales
Family: Apocynaceae
Genus: Asclepias
A. syriaca
Binomial name
Asclepias syriaca

Asclepias syriaca, commonly called common milkweed, butterfly flower, silkweed, silky swallow-wort, and Virginia silkweed, is a species of flowering plant.[1][2] It is native to southern Canada and much of the United States east of the Rocky Mountains, excluding the drier parts of the prairies.[3] It is in the genus Asclepias, the milkweeds. It grows in sandy soils as well as other kinds of soils in sunny areas.



A. syriaca is a clonal perennial forb growing up to 1.8 m (5 ft 11 in) tall.[4] Individual plants grow from rhizomes. All parts of common milkweed plants produce a white latex when cut. The simple leaves are opposite, sometimes whorled; broadly ovate-lanceolate. They grow to 10–28 cm (4–11 in) long and 4–12 cm (1+124+34 in) broad,[4] usually with entire, undulate margins and reddish main veins. They have very short petioles and velvety undersides.

The highly fragrant, nectariferous flowers vary from white (rarely) through pinkish and purplish and occur in umbellate cymes.[5][6] Individual flowers are about 1 cm (0.4 in) in diameter, each with five horn-like hoods and five pollinia. The seeds, each with long, white flossy hairs, occur in large follicles. Fruit production from self-fertilization is rare. In three study plots, outcrossed flowers had an average of about 11% fruit set.[7]



More than 450 insect species feed on A. syriaca, including flies, beetles, ants, bees, wasps, and butterflies; it is among the most important food sources for monarch butterfly caterpillars (Danaus plexippus) in the northeastern and midwestern United States; other species that feed on the plant include red milkweed beetle (Tetraopes tetraophthalmus), the milkweed tussock caterpillar (Euchaetes egle) and Oncopeltus fasciatus and Lygaeus kalmii.[2] Many kinds of insects visit A. syriaca flowers, and some kinds pollinate them, including Apis mellifera, the Western honey bee, and native Bombus spp. (bumblebees).[8] In the U.S. mid-Atlantic region, the introduced species A. mellifera was found to be the most "effective" pollinator, but this occurs more often among flowers of the same plant; since A. syriaca has a high level of self-incompatibility, it is less effective than Bombus spp. in the fertilization of flowers because Bombus are more likely to visit unrelated individuals.[9]

Monarch butterfly larvae consume primarily milkweeds, and monarch populations may decline when milkweeds are eliminated with herbicides.[10] The development and widely adopted cultivation of herbicide-resistant staple crops such as corn and soybeans have led to a massive reduction in weeds and native plants such as milkweeds.[11] Consequently, this has played a significant part in the population decline of the monarch butterfly. In 2018 the CEO of the National Wildlife Federation stated that the population of the monarch butterfly is now down 90 percent in the last 20 years and cited the reduction in milkweed as a contributing factor.[12]

Many parts of the United States face a reduction in milkweed population due to factors such as increased habitat loss due to development, roadside median mowing, and herbicide use.[13] Despite this, deforestation due to human settlement may have expanded the range and density of common milkweed in some regions.[14] Common milkweed has even become invasive as it is naturalized in several areas outside of its original native range, including Oregon and some parts of Europe. Since 2017, common milkweed has been listed as an invasive species in the European Union,[15] making the import and trade of the species forbidden in the whole of the European Union.[16] It has been naturalized in 23 countries worldwide.[17]

Over 40 distinct pathogens of Asclepias species have been identified, including two dozen pathogens for A. syriaca.[18] For example, milkweed yellows is an infectious disease caused by the milkweed yellows phytoplasma, a strain of bacteria distinguished by the absence of a cell wall.



A. syriaca can become aggressive.[1] It spreads aggressively from rhizomes and may not be suited to small gardens and formalized plantings.[19][20] The plant is winter hardy in USDA zones 3–9; it has a preference for moist but well drained soils, but is tolerant of dry conditions and clay soils.[21] It is ideal in semi-dry places where it can spread without presenting problems for other ornamental species.[1]

Monarch Watch provides information on rearing monarchs and their host plants.[22] Efforts to restore falling monarch butterfly populations by establishing butterfly gardens and monarch migratory "waystations" require particular attention to the target species' food preferences and population cycles, as well to the conditions needed to propagate and maintain their food plants.[23][24]

In the northeastern United States, monarch reproduction peaks in late summer when most of the plant's leaves are old and tough. Plants that are mowed or cut back in June – August regrow rapidly from their rhizomes in time for peak monarch egg-laying, when reproducing female monarchs have a preference for quickly-growing A. syriaca shoots whose foliage is tender and soft.[25]

A. syriaca is easily propagated by both seed and rhizome cuttings.[1] A U.S. Department of Agriculture conservation planting guide for Maryland recommends that, for optimum wildlife and pollinator habitat in mesic sites (especially for monarchs), a seed mix should contain 6.0% A. syriaca by weight and 2.0% by seed.[26] The plant's seeds require a period of cold treatment (cold stratification) before they will germinate.[27]

To protect seeds from washing away during heavy rains and from seed–eating birds, one can cover the seeds with a light fabric or with an 0.5 in (13 mm) layer of straw mulch.[28][29] However, mulch acts as an insulator. Thicker layers of mulch can prevent seeds from germinating if they prevent soil temperatures from rising enough when winter ends. Further, few seedlings can push through a thick layer of mulch.[30] Both seedlings and cuttings will usually bloom in their second year, although cuttings will occasionally bloom during their first year.[1]

The nonnative Aphis nerii (oleander aphid) can become abundant on milkweed shoots.[31]



The plant's latex contains large quantities of cardiac glycosides, making the leaves and stems of old tall plants toxic to humans and large animals.[32][33] The young shoots, young leaves, flower buds and immature fruits are all edible raw.[34]

Euell Gibbons, the author of Stalking the Wild Asparagus (1962), wrote that milkweed is bitter and toxic. However, he may have inadvertently prepared common dogbane (Apocynum cannabinum), a poisonous somewhat similar-looking plant instead. Gibbons devised a method to remove the bitterness and toxicity by plunging the young shoots into boiling water and cooking for one minute, repeating the procedure at least three times to make the plant safe to eat. Some modern foragers consider the bitterness and toxicity issue a myth. The plants have no bitterness when tasted raw, and can be cooked like asparagus, with no special processing.[34]

The plant has been studied as a source of rubber from the latex of the plant,[35] and as a fiber source from the seed fluff. The fluffy seed hairs have been used as the traditional background for mounted butterflies and other insects. The compressed floss has a silk-like sheen. The plant has also been explored for commercial use of its bast (inner bark) fiber, which is both strong and soft. U. S. Department of Agriculture studies in the 1890s and 1940s found that common milkweed has more potential for commercial processing than any other indigenous bast fiber plant, with estimated yields as high as hemp and quality as good as flax. Both the bast fiber and the floss were used historically by Native Americans for cordage and textiles. Milkweed has also been cultivated commercially to be used as insulation in winter coats.[36]

Traditionally, in both North America and Europe, the plant was used to treat respiratory infections such as pleurisy.[37]



The genome of A. syriaca has been sequenced.[14][38][39] Genomic analysis of several hundred different A. syriaca plants from throughout the species natural range in eastern North America showed that this species is a single panmictic population that experienced expansions about 12,000 years ago, after the recession of North American glaciers, and more recently, about 200 years ago, during clearing of forests for agriculture in the eastern United States.[14]



  1. ^ a b c d e Stevens, Michelle. "Plant guide for common milkweed (Asclepias syriaca)" (PDF). United States Department of Agriculture: Natural Resources Conservation Service: National Plant Data Center. Archived (PDF) from the original on July 5, 2021. Retrieved July 5, 2021.
  2. ^ a b Taylor, David. "Common Milkweed (Asclepias syriaca L.)". Plant of the Week. United States Department of Agriculture, United States Forest Service. Archived from the original on January 22, 2023. Retrieved December 24, 2023.
  3. ^ "Plants Profile for Asclepias syriaca (common milkweed)". plants.usda.gov. Retrieved January 2, 2021.
  4. ^ a b Elias, Thomas S.; Dykeman, Peter A. (2009) [1982]. Edible Wild Plants: A North American Field Guide to Over 200 Natural Foods. New York: Sterling. p. 106. ISBN 978-1-4027-6715-9. OCLC 244766414.
  5. ^ Liede, Sigrid; Weberling, Focko (1995). "On the inflorescence structure of Asclepiadaceae". Plant Systematics and Evolution. 197 (1–4): 99–109. Bibcode:1995PSyEv.197...99L. doi:10.1007/BF00984635. JSTOR 23642939. S2CID 28917929.
  6. ^ Lawrence, George H. M (1951). Taxonomy of vascular plants. Macmillan. OCLC 1151341689.[page needed]
  7. ^ Sparrow, F. K.; Pearson, N. L. (1948). "Pollen compatibility in Asclepias syriaca". Journal of Agricultural Research. 77: 187–199.
  8. ^ MacIvor, James Scott; Roberto, Adriano N.; Sodhi, Darwin S.; Onuferko, Thomas M.; Cadotte, Marc W. (2017). "Honey bees are the dominant diurnal pollinator of native milkweed in a large urban park". Ecology and Evolution. 7 (20): 8456–8462. Bibcode:2017EcoEv...7.8456M. doi:10.1002/ece3.3394. ISSN 2045-7758. PMC 5648680. PMID 29075462.
  9. ^ Howard, Aaron F; Barrows, Edward M (2014). "Self-pollination rate and floral-display size in Asclepias syriaca (Common Milkweed) with regard to floral-visitor taxa". BMC Evolutionary Biology. 14 (1): 144. Bibcode:2014BMCEE..14..144H. doi:10.1186/1471-2148-14-144. PMC 4080991. PMID 24958132.
  10. ^ Pleasants, John M.; Oberhauser, Karen S. (March 2013). "Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population: Herbicide use and monarch butterflies". Insect Conservation and Diversity. 6 (2): 135–144. doi:10.1111/j.1752-4598.2012.00196.x. S2CID 14595378.
  11. ^ Arnold, Carrie (December 21, 2018). "We're losing monarchs fast—here's why". National Geographic. Archived from the original on December 23, 2018.
  12. ^ "Monarch Butterfly 2018 Population Down by 14.8 Percent". The National Wildlife Federation Blog. March 7, 2018. Retrieved January 2, 2021.
  13. ^ Daniels, Jaret; Kimmel, Chase; McClung, Simon; Epstein, Samm; Bremer, Jonathan; Rossetti, Kristin (December 2018). "Better Understanding the Potential Importance of Florida Roadside Breeding Habitat for the Monarch". Insects. 9 (4): 137. doi:10.3390/insects9040137. PMC 6315611. PMID 30314302.
  14. ^ a b c Boyle, John H.; Strickler, Susan; Twyford, Alex; Ricono, Angela; Powell, Adrian; Zhang, Jing; Xu, Hongxing; Dalgleish, Harmony J.; Jander, Georg; Agrawal, Anurag A.; Puzey, Joshua R. (February 28, 2022). "Temporal matches and mismatches between monarch butterfly and milkweed population changes over the past 12,000 years". bioRxiv. Cold Spring Harbor Laboratory. doi:10.1101/2022.02.25.481796. S2CID 247170698.
  15. ^ "List of Invasive Alien Species of Union concern". November 29, 2023.
  16. ^ "REGULATION (EU) No 1143/2014 of the European parliament and of the council of 22 October 2014 on the prevention and management of the introduction and spread of invasive alien species".
  17. ^ Szilassi, Péter; Szatmári, Gábor; Pásztor, László; Árvai, Mátyás; Szatmári, József; Szitár, Katalin; Papp, Levente (December 12, 2019). "Understanding the Environmental Background of an Invasive Plant Species (Asclepias syriaca) for the Future: An Application of LUCAS Field Photographs and Machine Learning Algorithm Methods". Plants. 8 (12): 593. doi:10.3390/plants8120593. ISSN 2223-7747. PMC 6963816. PMID 31842272.
  18. ^ Borders, B.; Lee-Mäder, E. (2014). Milkweeds: A Conservation Practitioner's Guide (PDF). Portland, OR: The Xerces Society for Invertebrate Conservation. Retrieved November 14, 2021.
  19. ^ Hayes, Rhonda Fleming (2016). "A Milkweed for Every Garden". Pollinator Friendly Gardening: Gardening for Bees, Butterflies, and Other Pollinators. Minneapolis: Voyageur Press. p. 88. ISBN 978-0-7603-4913-7. LCCN 2015020836. OCLC 935530887 – via Google Books.
  20. ^ Abugattas, Alonzo (January 3, 2017). "Monarch Way Stations". Capital Naturalist. Archived from the original on March 8, 2021. Retrieved July 5, 2021 – via Blogger. The local monarch favorite is Common Milkweed (A. syriaca), but this may not be the best for a formal setting since they spread by underground stolons and so will not "stay" where they are planted.
  21. ^ "Common milkweed". The Morton Arboretum. Archived from the original on April 18, 2016. Retrieved January 5, 2021.
  22. ^ "Monarch Watch". monarchwatch.org. Retrieved September 27, 2015.
  23. ^ Borders, Brianna; Lee–Mäder, Eric (2014). "Milkweed Propagation and Seed Production" (PDF). Milkweeds: A Conservation Practitioner's Guide: Plant Ecology, Seed Production Methods, and Habitat Restoration Opportunities. Portland, Oregon: The Xerces Society for Invertebrate Conservation. pp. 21–95. Archived (PDF) from the original on July 4, 2021. Retrieved July 12, 2021.
  24. ^ Landis, Thomas D.; Dumroese, R. Kasten (2015). "Propagating Native Milkweeds for Restoring Monarch Butterfly Habitat" (PDF). International Plant Propagators' Society, Combined Proceedings (2014). 64: 299–307. Archived (PDF) from the original on March 8, 2021. Retrieved July 11, 2021 – via United States Department of Agriculture: United States Forest Service.
  25. ^ Multiple sources:
    • National Academies of Sciences, Engineering, and Medicine (2020). Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies. Washington, D.C.: National Academies Press. pp. 79–80. doi:10.17226/25693. ISBN 9780309481328. LCCN 2020935714. OCLC 1229163481. S2CID 218854539. National Cooperative Highway Research Program (NCRHP) Research Report 942. Archived from the original on July 29, 2020. Retrieved July 8, 2021. Could roadside mowing stimulate milkweed growth and support monarch breeding? Limited research in eastern North America has shown that spring or summer mowing can promote new growth and extend the availability of milkweed plants for monarch breeding. Mowing may stimulate growth of some milkweed species, particularly those that spread through rhizomes like common milkweed (A. syriaca) and showy milkweed (A. speciosa). .... However, more research is needed in other areas to determine the optimal timing and frequency of mowing that promotes not only milkweed but also nectar plants. It is also unknown if the benefit of additional milkweed availability in the fall outweighs the costs of the larval mortality caused by summer mowing. The benefits are likely greater in areas that primarily have breeding monarchs in the spring and fall and where the dominant species of milkweed spread by rhizomes. Sources: Alcock et al. 2016; Baum and Mueller, 2015; Bhowick 1994; Haan and Landis 2019; Fischer et al. 2015{{cite book}}: CS1 maint: multiple names: authors list (link)
    • Higgins, Adrian (May 27, 2015). "A gardener's guide to saving the monarch". Home & Garden. The Washington Post. Archived from the original on May 31, 2015. Retrieved October 17, 2020. "The monarch doesn't care where the milkweed grows, and putting it in residential neighborhoods makes perfect sense," said Doug Tallamy, an entomologist at the University of Delaware, author and expert on wildlife habitat gardens. ....
      The Smithsonian Institution's Butterfly Habitat Garden .... and the Ripley Garden .... are both good places to see milkweed integrated into a garden setting.
      At the butterfly garden, you can see the common milkweed ... now looking pretty good in fresh, unblemished clumps. By late summer, it looks tall, tired and tough. Tallamy says if you grow it, you should cut it back at least by half in June to produce soft foliage in late summer that will be more munchable for the caterpillars. If you do that, make sure there are no larvae on the plant before you chop it.
    • Abugattas, Alonzo (January 3, 2017). "Monarch Way Stations". Capital Naturalist. Archived from the original on March 8, 2021. Retrieved July 5, 2021 – via Blogger. Virginia is blessed for instance with 13 native Asclepias species plus 4 climbing vines that Monarch caterpillars can feed on. For the best results, cut the some of the stems back in late summer after they've bloomed. Fall is the when we get the most Monarchs laying eggs on our milkweeds. Since the mother butterflies prefer young, more tender growth, you can provide this by timing your pruning so there are new leaves by September or so for the arriving Monarchs. Just make sure to leave a few to produce pods for seeds. The local monarch favorite is Common Milkweed (A. syriaca), .....
    • Gomez, Tony. "Asclepias syriaca: Common Milkweed for Monarch Caterpillars". Monarch Butterfly Garden. MonarchButterflyGarden.net. Archived from the original on March 16, 2015. Retrieved October 17, 2010. Cut- At mid season after the blooms have faded, cut some common plants back by about a third. This promotes fresh plant growth and could get you an extra generation of monarchs on the fresh new leaves. Leave some plants uncut if you want to harvest milkweed seeds in fall.
    • Stevens, Michelle. "Plant guide for common milkweed (Asclepias syriaca)" (PDF). United States Department of Agriculture: Natural Resources Conservation Service: National Plant Data Center. Archived (PDF) from the original on July 5, 2021. Retrieved July 5, 2021.
  26. ^ United States Department of Agriculture (December 2022). "Maryland Conservation Planting Guide" (PDF). Mix 16: High Diversity Native Grass/Forb Mix for Mesic Sites. p. 19. Archived (PDF) from the original on January 6, 2024. This mix has a predominant wildflower component for optimum wildlife and pollinator habitat.
  27. ^ Multiple sources:
  28. ^ Mader, Eric; Shepherd, Mathew; Vaughan, Mace; Black, Scott Hoffman; LeBuhn, Gretchen (2011). Establishing Pollinator Habitat from Seed: Sowing Seed. North Adams, Massachusetts: Storey Publishing. pp. 113–114. ISBN 9781603427470. LCCN 2010043054. OCLC 776997073. Retrieved July 7, 2021 – via Internet Archive. {{cite book}}: |work= ignored (help)
  29. ^ Landis, Thomas D.; Dumroese, R. Kasten (2015). "Propagating Native Milkweeds for Restoring Monarch Butterfly Habitat: Propagating Native Milkweeds: Seed Propagation" (PDF). International Plant Propagators' Society, Combined Proceedings (2014). 64: 302. Archived (PDF) from the original on March 8, 2021. Retrieved July 11, 2021 – via United States Department of Agriculture: United States Forest Service. Any of the standard seed propagation methods (Landis et al., 1999) are effective with milkweed. Direct sowing of non-stratified seeds during the fall followed by exposure to ambient winter conditions can be effective, but the seeds must be mulched and protected. Cover sown seeds with a thin mulch; research has found that common milkweed seeds germinated better when planted 1 to 2 cm (0.4 to 0.8 in.) deep than when at the soil surface (Jeffery and Robison, 1971).
  30. ^ Bush-Brown, James; Bush-Brown, Louise (1958). "Chapter 32: Mulches". America's garden book. New York: Charles Scribner's Sons. p. 768. LCCN 58005738. OCLC 597041748 – via Internet Archive.
  31. ^ Higgins, Adrian (May 27, 2015). "7 milkweed varieties and where to find them". Home & Garden. The Washington Post. Archived from the original on September 26, 2020. Retrieved October 17, 2020.
  32. ^ "Asclepias". ScienceDirect. Archived from the original on July 10, 2021. Retrieved July 10, 2021.
  33. ^ Everest, Michael A.; Gonella, Michael P.; Bowler, Holly G.; Waschak, Joshua R. (August 6, 2019). "How Toxic is Milkweed when Harvested and Cooked according to Myaamia Tradition?". Ethnobiology Letters. 10 (1). Society of Ethnobiology: 50–56. doi:10.14237/ebl.10.1.2019.1487. Asclepias syriaca L. (common milkweed) is known to contain sufficient amounts of cardiac glycosides, which are known to be toxic to humans.
  34. ^ a b Thayer, S. (2006). The Forager's Harvest. Forager's Harvest. pp. 290–305. ISBN 0-9766266-0-8. LCCN 2005911400. OCLC 1229125866.
  35. ^ Bowers, Janice Emily (1990). Natural Rubber-producing Plants for the United States. National Agricultural Library.
  36. ^ Bernstein, Jaela (October 13, 2016). "How a Quebec company used a weed to create a one-of-a-kind winter coat". CBC News. Retrieved January 5, 2018.
  37. ^ Lyle, Katie Letcher (2010) [2004]. The Complete Guide to Edible Wild Plants, Mushrooms, Fruits, and Nuts: How to Find, Identify, and Cook Them (2nd ed.). Guilford, CN: FalconGuides. p. 23. ISBN 978-1-59921-887-8. OCLC 560560606.
  38. ^ Weitemier, Kevin; Straub, Shannon C.K.; Fishbein, Mark; Bailey, C. Donovan; Cronn, Richard C.; Liston, Aaron (September 20, 2019). "A draft genome and transcriptome of common milkweed ( Asclepias syriaca ) as resources for evolutionary, ecological, and molecular studies in milkweeds and Apocynaceae". PeerJ. 7: e7649. doi:10.7717/peerj.7649. ISSN 2167-8359. PMC 6756140. PMID 31579586.
  39. ^ Straub, Shannon CK; Fishbein, Mark; Livshultz, Tatyana; Foster, Zachary; Parks, Matthew; Weitemier, Kevin; Cronn, Richard C; Liston, Aaron (2011). "Building a model: developing genomic resources for common milkweed (Asclepias syriaca) with low coverage genome sequencing". BMC Genomics. 12 (1): 211. doi:10.1186/1471-2164-12-211. ISSN 1471-2164. PMC 3116503. PMID 21542930.



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