Asclepias syriaca (common milkweed)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Plant Type
- Distribution Table
- Habitat List
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Biology and Ecology
- Soil Tolerances
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Pathway Causes
- Pathway Vectors
- Impact Summary
- Economic Impact
- Environmental Impact
- Risk and Impact Factors
- Uses List
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Asclepias syriaca Blanco, 1837
Preferred Common Name
- common milkweed
Other Scientific Names
- Asclepias cornuti Decne.
- Asclepias intermedia Vail
- Asclepias kansana Vail
- Asclepias syriaca L. var. kansana (Vail) Palmer & Steyermark
International Common Names
- English: broadleaf milkweed; butterfly flower; cotton weed; silkweed; silky milkweed; silky swallow-wort; Virginia silkweed milkweed; wild cotton
- Spanish: asclepia; vencetosigo comun
- French: asclepiade; asclepiade de Syrie; cotonnier; petit-cochon
Local Common Names
- Germany: Gehoernte Seidenpflanze
- Netherlands: zijdeplant
- ASCSY (Asclepias syriaca)
Summary of InvasivenessTop of page
A. syriaca can be an aggressive and persistent weed and contains several poisonous glucosidic substances (cardenolides) known to be poisonous to sheep, cattle, and occasionally horses (Anderson, 1999).
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Gentianales
- Family: Asclepiadaceae
- Genus: Asclepias
- Species: Asclepias syriaca
Notes on Taxonomy and NomenclatureTop of page
Asclepias is a widespread genus with 76 species and 91 accepted taxa overall. There are 14 species of milkweed native in Canada (White, 1996). A. syriaca is the most widespread and locally abundant species of the genus (Hartzler and Buhler, 2000); it occurs in 38 states of North America.
According to Endress and Bruyns (2000) Asclepiadaceae is now treated as sub-family Asclepiadoideae in the family Apocynaceae.
DescriptionTop of page
A. syriaca (common milkweed) is a perennial herb with long-spreading rhizomes. Stems stout, erect, to 2 m tall, with short downy hairs and milky juice; leaves opposite, smooth margined, oblong, 10-20 cm long and 5-11 cm wide, with prominent veins; upper surface smooth, lower covered with short white hairs. Flowers sweet-smelling, pink to white, in large, many-flowered (the number per inflorescence varies greatly, from less than 10 to more than 120) axillary and apical bell-like clusters. The long-lived flowers produce copious amounts of nectar (Wyatt and Broyles, 1994), flowering from June to August, depending on initial growth, climate, and location (Anderson, 1999). Seed brown, flat, oval, 6 mm long, 5 mm wide, with a tuft of silky white hairs apically. All plant parts contain latex; shoots from established plants arise from adventitious root buds, emerging in April and May. The root system is composed of horizontal and vertical roots. In established stands, vertical roots may penetrate the soil to depths of 3.8 m (Anderson, 1999).
Plant TypeTop of page Herbaceous
DistributionTop of page
Contrary to its specific name, A. syriaca is native to northeastern, north central and southeastern United States and adjacent areas of Canada, and has spread to cultivated areas (Hartzler Buhler, 2000). This plant grows throughout the Great Plains ecoregion from southern Canada south to northeastern Oklahoma, northwestern Georgia, and Texas; and east from North Carolina to Maine (USDA-NRCS, 2010). It is naturalized in cultivated ground and dry grassland in various parts of central and southern Europe (IENICA, 2003).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
HabitatTop of page
A. syriaca colonizes a variety of communities from woodlands to cleared grasslands and marshlands. It grows in clumps or patches in meadows, fencerows, roadsides, railways, waste places, reduced-tillage fields, and other open habitats.
Habitat ListTop of page
|Terrestrial – Managed||Cultivated / agricultural land||Principal habitat||Harmful (pest or invasive)|
|Managed grasslands (grazing systems)||Present, no further details||Harmful (pest or invasive)|
|Disturbed areas||Principal habitat||Harmful (pest or invasive)|
|Rail / roadsides||Principal habitat||Harmful (pest or invasive)|
|Terrestrial ‑ Natural / Semi-natural||Natural grasslands||Present, no further details||Harmful (pest or invasive)|
Hosts/Species AffectedTop of page
The crops most affected by this species are soybeans, corn, peanuts and grain sorghum (Anderson, 1999) and maize (Konstantinovic et al., 2008). Canadian studies of competition between common milkweed and oats found up to 20% yield loss of grain (Bhowmik, 1982).
Host Plants and Other Plants AffectedTop of page
Biology and EcologyTop of page
A. syriaca is genetically self-incompatible, although low-levels of self-compatibility have been reported (Wyatt and Broyles, 1994), and this species has an unusual late-acting form of ovarian rejection. Flowers are self-sterile and insect-pollinated (Anderson, 1999), and pollen dispersal via a pollinium results with a fruit sharing the same outcrossed paternal parent (Hochwender, 2000). Only around 2% of the flowers produce mature pods, with an average plant producing 4-6 pods, containing approx. 150-425 seeds.
A. syriaca has a pollen delivery system whereby packets of pollen (pollinia) are transferred as a single unit during pollination; this method of reproduction is only seen elsewhere in some members of the Orchidaceae (Pleasants, 1991).The vegetative habit and weedy reproductive strategy A. syriaca makes it one of the most distinct milkweeds (Wilbur, 1976).
In a study using isozyme polymorphisms to study multiple paternity in A. syriaca, Gold and Shore (1995) found no statistical evidence for multiple paternity within fruits but extensive multiple paternity between fruits on the same ramet, suggesting potential choice of mates through selective fruit abortion.
Physiology and Phenology
A. syriaca grows as a colony of plants and each colony develops from a single plant arising from a seed or root segment, it has underground rootstocks that develop adventitious buds which give rise to new individuals; a large clonal group can comprise several thousand stems (Wilbur, 1976).
Vertebrate herbivores browse A. syriaca and results from a study by Hochwender (2000), showed that in low nutrient conditions, this species allocates resources to the storage organ, providing greater biomass when damaged; therefore an ability to compensate for damage might be important for this species.
A. syriaca is adapted to wide range of climatic and edaphic conditions and will tolerate soil conditions in any textural group, but is most commonly found on well-drained soils of loamy texture and grows best in full sunlight or light shade. It does not tolerate excessive moisture. A. syriaca has been found to be the most abundant invasive species in open sand grasslands (Botta-Dukat, 2008).
ClimateTop of page
|C - Temperate/Mesothermal climate||Preferred||Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C|
Soil TolerancesTop of page
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
|Aphis nerii||Herbivore||to genus|
|Danaus plexippus||Herbivore||to genus|
|Labidomera clivicollis||Herbivore||to genus|
|Liriomyza asclepiadis||Herbivore||to genus|
|Lygaeus kalmii||Herbivore||to genus|
|Rhyssomatus lineaticollis||Herbivore||to genus|
|Tetraopes tetrophthalmus||Herbivore||to genus|
Notes on Natural EnemiesTop of page
Approximately 12 species of herbivore consume A. syriaca in eastern North America and nearly all are specialists of Asclepias spp. because of particular mandibular structures, feeding modes, and the way they avoid the defensive latex production of this species (Van Zandt and Agrawal, 2004).
Means of Movement and DispersalTop of page
Natural Dispersal (Non-Biotic)
Only 3% of A. syriaca flowers produce seed pods, as most fall from the inflorescence approximately 10 days after opening (Anderson, 1999). A. syriaca spreads mainly by seeds which are wind pollinated and are dispersed on tufts of floss(Bhowmik, 1982). A. syriaca can produce large numbers of seeds, especially compared to other milkweed species, which facilitates dispersal over a long distance (White, 1996). Contrary to this, however, Pleasants (1991) found that much pollen dispersal in this species was short-distance.
Pathway CausesTop of page
|Research||Yes||Gaertner, 1979, publ. 1980|
Pathway VectorsTop of page
Impact SummaryTop of page
|Environment (generally)||Positive and negative|
Economic ImpactTop of page
Losses due to this species have been recorded in Sorghum production as A. syriaca populations increased (NAPPO, 2003). The floss attached to seeds also tends to clog air intake devices on combines during harvest (Anderson, 1999).
Environmental ImpactTop of page
Impact on Biodiversity
A. syriaca can be an aggressive and persistent weed and contains several poisonous glucosidic substances (cardenolides) known to be poisonous to sheep, cattle, and occasionally horses (Anderson, 1999). All parts of the plant contain the potentially toxic substances and A. syriaca is toxic to poultry; some milkweeds have been declared ‘noxious weeds’ in some North America states (White, 1996).
The specialist herbivores Tetraopes tetraophthalmus and Danaus plexippus have developed adaptations that allow them to sequester plant-generated cardenolides to defend themselves against predators (Hochwender et al., 2000).
Populations of the plant are thought to be beneficial as a source of nectar for butterflies, bees and other insects and A. syriaca plays an important part in the life cycle of the monarch butterfly (Danaus plexippus). Since D. plexippus requires A. syriaca as a larval food (Urquhart and Urquhart, 1979), D. plexippus might be at risk in Canada if noxious weed legislation were to be enforced and resulted in the elimination of milkweed (Hartzler and Buhler, 2000).
Risk and Impact FactorsTop of page Invasiveness
- Invasive in its native range
- Proved invasive outside its native range
- Has a broad native range
- Abundant in its native range
- Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
- Pioneering in disturbed areas
- Has high reproductive potential
- Reproduces asexually
- Negatively impacts agriculture
- Negatively impacts animal health
- Causes allergic responses
UsesTop of page
A. syriaca is considered medicinal in the USA and foliage or latex is used as a remedy for cancer, tumours and warts. It is also thought to be beneficial in treating asthma, catarrh and cough. Good quality fibre is obtained from the inner bark of the stem and can be used to make twine.
Uses ListTop of page
- Wildlife habitat
Human food and beverage
Similarities to Other Species/ConditionsTop of page
A. speciosa (showy milkweed) is similar to A. syriaca but it has broad, oval and rounded or heart-shaped leaves, densely woolly stalks, and fewer and longer flowers. Apocynum cannabinum (hemp dogbane) could be confused with A. syriaca but can be distinguished by its narrow, elliptical leaves 5-12 cm long, which are not hairy (Anderson, 1999). A. tuberosa (butterfly-weed) can also be mistaken for A. syriaca; it looks similar but it has orange flowers and the sap is not as milky.
Prevention and ControlTop of page
Removal of stalks by cutting can aggravate the problem as this stimulates growth from underground buds, and when cultivated, the resulting small root fragments will grow into a new plant.
Seedlings can be controlled with selected herbicides as pre-emergence treatments Bhowmik (1982).Aboveground plant parts may be destroyed by herbicides including 2, 4-D, mecoprop, dicamba and MCPA, but growth of adventitious roots is stimulated by this action. Amitrole-T and glyphosate will kill top growth and result in restricted regrowth during the following season. Glyphosate seems to be most effective overall and may reduce A. syriaca occurrence in crop fields (NAPPO, 2003).
ReferencesTop of page
GBIF, 2010. Global Biodiversity Information Facility. Global Biodiversity Information Facility. GBIF. http://data.gbif.org/species/
IENICA, 2003. Milkweed, Interactive European Network for Industrial Crops and their Applications (IENICA). Milkweed, Interactive European Network for Industrial Crops and their Applications (IENICA). http://www.ienica.net/crops/milkweed.pdf
Konstantinovic B; Meseldzija M; Mandic N, 2008. Distribution of Asclepias syriaca L. on the territory of Vojvodina and possibilities of its control. Herbologia, 9(2):39-46. http://www.anubih.ba/index.php?option=content&lang=eng&Theme=herbologia&Level=2&ItemID=7
White DJ, 1996. Status, distribution, and potential impact from noxious weed legislation. Report prepared for the Canadian Wildlife Service, Ottawa, Canada. Status, distribution, and potential impact from noxious weed legislation. Report prepared for the Canadian Wildlife Service, Ottawa, Canada. http://www.monarchwatch.com/read/articles/canweed1.htm
Zandt PAvan; Agrawal AA, 2004. Community-wide impacts of herbivore-induced plant responses in milkweed (Asclepias syriaca). Ecology, 85(9):2616-2629. http://www.esajournals.org/perlserv/?request=get-document&doi=10.1890%2F03-0622
ContributorsTop of page
01/03/10 Original text by:
Claire Teeling, Consultant, UK
Distribution MapsTop of page
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