Asclepias

Asclepias is a genus of herbaceous, perennial, flowering plants known as milkweeds, named for their latex, a milky substance containing cardiac glycosides termed cardenolides, exuded where cells are damaged.[3][4][5] Most species are toxic to humans and many other species, primarily due to the presence of cardenolides, although, as with many such plants, there are species that feed upon them (i.e. leaves) and from them (i.e. nectar). The genus contains over 200 species distributed broadly across Africa, North America, and South America.[6] It previously belonged to the family Asclepiadaceae, which is now classified as the subfamily Asclepiadoideae of the dogbane family, Apocynaceae.

"Milkweed" redirects here. For other uses, see Milkweed (disambiguation).

Not to be confused with Asclepius.

Asclepias
Asclepias syriaca showing flowers and latex
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Gentianales
Family:	Apocynaceae
Subfamily:	Asclepiadoideae
Tribe:	Asclepiadeae
Subtribe:	Asclepiadinae
Genus:	Asclepias L.[1]
Type species
Asclepias syriaca L.
Species[2]
Asclepias albens Asclepias albicans Asclepias alticola Asclepias ameliae Asclepias amplexicaulis Asclepias angustifolia Asclepias arenaria Asclepias asperula Asclepias asperula subsp. asperula Asclepias asperula subsp. capricornu Asclepias atroviolacea Asclepias aurea Asclepias auriculata Asclepias barjoniifolia Asclepias boliviensis Asclepias brachystephana Asclepias brevipes Asclepias californica Asclepias californica subsp. californica Asclepias californica subsp. greenei Asclepias candida Asclepias aff. candida Fishbein 6347 Asclepias cinerea Asclepias circinalis Asclepias connivens Asclepias cordifolia Asclepias coulteri Asclepias crispa Asclepias cryptoceras Asclepias cryptoceras subsp. cryptoceras Asclepias cryptoceras subsp. davisii Asclepias cucullata Asclepias cultriformis Asclepias curassavica Asclepias curtissii Asclepias cutleri Asclepias densiflora Asclepias disparilis Asclepias eastwoodiana Asclepias elata Asclepias elegantula Asclepias emoryi Asclepias engelmanniana Asclepias eriocarpa Asclepias erosa Asclepias exaltata Asclepias fascicularis Asclepias feayi Asclepias flava Asclepias foliosa Asclepias fournieri Asclepias fulva Asclepias gentryi Asclepias gibba Asclepias glaucescens Asclepias grandirandii Asclepias hallii Asclepias hirtella Asclepias humistrata Asclepias hypoleuca Asclepias inaequalis Asclepias incarnata Asclepias incarnata subsp. incarnata Asclepias incarnata subsp. pulchra Asclepias involucrata Asclepias jaliscana Asclepias jorgeana Asclepias labriformis Asclepias lanceolata Asclepias lanuginosa Asclepias latifolia Asclepias lemmonii Asclepias leptopus Asclepias linaria Asclepias linearis Asclepias longifolia Asclepias lynchiana Asclepias macropus Asclepias macrosperma Asclepias macrotis Asclepias macroura Asclepias masonii Asclepias mcvaughii Asclepias meadii Asclepias melantha Asclepias mellodora Asclepias mellodora var. mellodora Asclepias mexicana Asclepias michauxii Asclepias mirifica Asclepias multicaulis Asclepias nivea Asclepias notha Asclepias nummularia Asclepias nyctaginifolia Asclepias obovata Asclepias oenotheroides Asclepias otarioides Asclepias ovalifolia Asclepias ovata Asclepias pedicellata Asclepias pellucida Asclepias perennis Asclepias phenax Asclepias pilgeriana Asclepias praemorsa Asclepias pratensis Asclepias pringlei Asclepias prostrata Asclepias puberula Asclepias pumila Asclepias purpurascens Asclepias quadrifolia Asclepias quinquedentata Asclepias randii Asclepias rosea Asclepias rubra Asclepias ruthiae Asclepias sanjuanensis Asclepias scaposa Asclepias schaffneri Asclepias scheryi Asclepias senecionifolia Asclepias similis Asclepias solanoana Asclepias solstitialis Asclepias speciosa Asclepias standleyi Asclepias stathmostelmoides Asclepias stellifera Asclepias stenophylla Asclepias subaphylla Asclepias subulata Asclepias subverticillata Asclepias sullivantii Asclepias syriaca Asclepias texana Asclepias tomentosa Asclepias tuberosa Asclepias tuberosa subsp. interior Asclepias tuberosa subsp. rolfsii Asclepias tuberosa subsp. tuberosa Asclepias uncialis Asclepias variegata Asclepias verticillata Asclepias vestita Asclepias vestita subsp. parishii Asclepias vestita subsp. vestita Asclepias vinosa Asclepias viridiflora Asclepias viridis Asclepias viridula Asclepias virletii Asclepias welshii Asclepias woodii Asclepias woodsoniana Asclepias zanthodacryon
Synonyms[1]
Acerates Elliott Anantherix Nutt. Asclepiodella Small Asclepiodora A.Gray Biventraria Small Oxypteryx Greene Podostemma Greene Podostigma Elliott (probable) Schizonotus A.Gray Solanoa Greene Trachycalymma (K.Schum.) Bullock (possible)

The genus was formally described by Carl Linnaeus in 1753,[7] who named it after Asclepius, the Greek god of healing.[8]

Milkweed flowers

Asclepias syriaca seed pods, upper image from August and lower from December

Milkweed sprout, a few days after sowing

Chemical structure of oleandrin, one of the cardiac glycosides

Members of the genus Asclepias produce some of the most complex flowers in the plant kingdom, comparable to orchids in complexity. Five petals reflex backwards revealing a gynostegium (fused stamen filaments and styles) surrounded by a five-membrane corona. The corona is composed of a five paired hood and horn structure with the hood acting as a sheath for the inner horn. Glands holding pollinia are found between the hoods. The size, shape and color of the horns and hoods are often important identifying characteristics for species in the genus Asclepias.[9]

Pollination in this genus is accomplished in an unusual manner. Pollen is grouped into complex structures called pollinia (or "pollen sacs"), rather than being individual grains or tetrads, as is typical for most plants. The feet or mouthparts of flower-visiting insects such as bees, wasps and butterflies, slip into one of the five slits in each flower formed by adjacent anthers. The bases of the pollinia then mechanically attach to the insect, so that a pair of pollen sacs can be pulled free when the pollinator flies off, assuming the insect is large enough to produce the necessary pulling force (if not, the insect may become trapped and die).[10] Pollination is effected by the reverse procedure, in which one of the pollinia becomes trapped within the anther slit. Large-bodied hymenopterans are the most common and best pollinators, accounting for over 50% of all Asclepias pollination[11], whereas monarch butterflies are poor pollinators of milkweed.[4]

male Pepsis grossa, a typical milkweed-pollinating wasp

Honeybee on antelope horn (Asclepias asperula) showing pollinia attached to legs

Asclepias species produce their seeds in pods termed follicles. The seeds, which are arranged in overlapping rows, bear a cluster of white, silky, filament-like hairs known as the coma[12] (often referred to by other names such as pappus, "floss", "plume", or "silk"). The follicles ripen and split open, and the seeds, each carried by its coma, are blown by the wind. Some, but not all, milkweeds also reproduced by clonal (or vegetative) reproduction.

Ecology

American milkweeds are an important nectar source for native bees, wasps, and other nectar-seeking insects, though non-native honey bees commonly get trapped in the stigmatic slits and die.[10][13] Milkweeds are also the larval food source for monarch butterflies and their relatives, as well as a variety of other herbivorous insects (including numerous beetles, moths, and true bugs) specialized to feed on the plants despite their chemical defenses.[4]

Milkweeds use three primary defenses to limit damage caused by caterpillars: hairs on the leaves, cardenolide toxins, and latex fluids. Data from a DNA study indicate that, generally, more recently-evolved milkweed species ("derived" in botany parlance) use these preventative strategies less but grow faster than older species, potentially regrowing faster than caterpillars can consume them.[14][15]

Research indicates that the very high cardenolide content of Asclepias linaria reduces the impact of the OE parasite, Ophryocystis elektroscirrha, on the monarch butterfly, Danaus plexippus. By contrast, some species of Asclepias are extremely poor sources of cardenolides, such as Asclepias fascicularis, Asclepias tuberosa, and Asclepias angustifolia.

Uses

Milkweed is not grown commercially in large scale, but the plant has had many uses throughout human history.[4] Milkweed has a long history of both medicinal, every day and, military use that most people aren’t even aware of.  The Omaha people, from Nebraska, the Menomin which were from Wisconsin and upper Michigan, the Dakota’s from Minnesota and, the Ponca people from Nebraska used it for a medicinal and everyday usage ages ago. They used it for everything from a diarrheic, relief from sore throats, it was chewed for swelling and rashes, new mothers that could not produce milk would drink it, it was used to treat colic, it was used to expel tapeworms, it was used to cure snakebite and for a contraceptive. Heart-leaf milkweed was used by the Miwok people of California for its stems, which they dried and used for cords such as strings and ropes.[16] The milkweed filaments from the coma (the "floss") are hollow and coated with wax, and have good insulation qualities. During World War II, more than 5,000 t (5,500 short tons) of milkweed floss was collected in the United States as a substitute for kapok.[17][18] Milkweed is grown commercially as a hypoallergenic filling for pillows[19] and as insulation for winter coats.[20]

A study of the insulative properties of various materials found that milkweed floss was outperformed by other materials in terms of insulation, loft, and lumpiness, but it scored well when mixed with down feathers.[21] Milkweed fibers are also used to clean up oil spills.[22]

Milkweed seeds

The bast fibers of some species can be used for rope. Milkweed latex contains about two percent latex and was attempted as a source of natural rubber by both Nazi Germany and the United States during World War II. No record has been found of large-scale success.

Asclepias is also known as "Silk of America"[23] which is a strand of common milkweed (Asclepias syriaca) gathered mainly in the valley of the Saint Lawrence River in Canada. The silk is used in thermal insulation, acoustic insulation, and oil absorbents.[24][25]

Milkweed also contains cardiac glycoside poisons that inhibit animal cells from maintaining a proper K⁺, Ca²⁺ concentration gradient.[5] As a result, many peoples of South America and Africa used arrows poisoned with these glycosides to fight and hunt more effectively. Milkweed is toxic and may cause death when animals consume large quantities of the plant. Milkweed also causes mild dermatitis in some who come in contact with it. Nonetheless, it can be made edible if properly processed.[4]

The leaves of Asclepias species are a food source for monarch butterfly larvae and some other milkweed butterflies.[4] These plants are often used in butterfly gardening and monarch waystations.[26]

However, some milkweed species are not suitable for butterfly gardens and monarch waystations. For example, Asclepias curassavica, or tropical milkweed, is often planted as an ornamental in butterfly gardens. Year-round plantings in the USA are controversial and criticised, as they may be the cause of new overwintering sites along the U.S. Gulf Coast, leading to year-round breeding of monarchs.[27] This is thought to adversely affect migration patterns, and to cause a dramatic buildup of the dangerous parasite, Ophryocystis elektroscirrha.[28] New research also has shown that monarch larvae reared on tropical milkweed show reduced migratory development (reproductive diapause), and when migratory adults are exposed to tropical milkweed, it stimulates reproductive tissue growth.[29]

Monarch caterpillars do not favor butterfly weed (Asclepias tuberosa) because the leaves of that milkweed species contain little toxin (cardiac glycosides). Some other milkweeds may have similar characteristics.

Species

Some Asclepias species:

	Asclepias albicans	Whitestem milkweed, native to the Mojave and Sonoran deserts
	Asclepias amplexicaulis	Blunt-leaved milkweed, native to central and eastern United States
	Asclepias asperula	Antelope horns, native to American southwest and northern Mexico
	Asclepias californica	California milkweed, native to central and southern California
	Asclepias cordifolia	Heart-leaf milkweed, native to the Sierra Nevada and Cascade Range up to 2000 m.
	Asclepias cryptoceras	Pallid milkweed, native to the western United States.
	Asclepias curassavica	Scarlet milkweed, tropical milkweed, bloodflower, bastard ipecacuanha, native to the American tropics, introduced to other continents
	Asclepias curtissii	Curtiss's milkweed, endemic to sandy areas of Florida
	Asclepias eriocarpa	Woollypod milkweed, native to California, Baja California, and Nevada
	Asclepias erosa	Desert milkweed, native to California, Arizona, and Baja California
	Asclepias exaltata	Poke milkweed, native to eastern North America
	Asclepias fascicularis	Narrow-leaf milkweed, native to Western United States
	Asclepias hirtella	Tall green milkweed
	Asclepias humistrata	Sandhill milkweed, native to southeastern United States
	Asclepias incarnata	Swamp milkweed, native to wetlands of North America
	Asclepias involucrata
	Asclepias lanceolata	Lanceolate milkweed (Cedar Hill milkweed), native to coastal plain of eastern United States from Texas to New Jersey
	Asclepias linaria	Pine needle milkweed, native to Mojave and Sonoran deserts
	Asclepias linearis	Slim milkweed
	Asclepias meadii	Mead's milkweed, native to midwestern United States
	Asclepias nivea
	Asclepias nyctaginifolia	Mojave milkweed, native to the American southwest
	Asclepias obovata	Pineland milkweed
	Asclepias purpurascens	Purple milkweed, native to eastern, southern, and midwestern United States
	Asclepias quadrifolia	Four-leaved milkweed, native to eastern United States and Canada
	Asclepias rubra	Red milkweed
	Asclepias solanoana	Serpentine milkweed, native to northern California
	Asclepias speciosa	Showy milkweed, native to western United States and Canada
	Asclepias subulata	Rush milkweed, leafless milkweed, native to southwestern North America
	Asclepias subverticillata	Horsetail milkweed[30]
	Asclepias sullivantii	Sullivant's milkweed
	Asclepias syriaca	Common milkweed
	Asclepias texana	Texas milkweed
	Asclepias tuberosa	Butterfly weed, pleurisy root
	Asclepias uncialis	Wheel milkweed
	Asclepias variegata	White milkweed
	Asclepias verticillata	Whorled milkweed
	Asclepias vestita	Woolly milkweed
	Asclepias viridiflora	Green milkweed
	Asclepias viridis	Green antelopehorn, spider milkweed
	Asclepias welshii	Welsh's milkweed

There are also 12 species of Asclepias in South America, among them: A. barjoniifolia, A. boliviensis, A. curassavica, A. mellodora, A. candida, A. flava, and A. pilgeriana.

Formerly classified species

Species formerly classified under the genus Asclepias include:

• Calotropis gigantea (L.) W.T.Aiton (as A. gigantea L.)
• Calotropis procera (Aiton) W.T.Aiton (as A. procera Aiton)
• Cynanchum louiseae Kartesz & Gandhi (as A. nigra L.)
• Cynanchum thesioides (Freyn) K.Schum. (as A. sibirica L.)
• Funastrum clausum (Jacq.) Schltr. (as A. clausa Jacq.)
• Gomphocarpus cancellatus (Burm.f.) Bruyns (as A. cancellatus Burm.f. or A. rotundifolia Mill.)
• Gomphocarpus fruticosus (L.) W.T.Aiton (as A. fruticosa L.)
• Marsdenia macrophylla (Humb. & Bonpl. ex Willd.) E.Fourn. (as A. macrophylla Humb. & Bonpl. ex Schult.)
• Marsdenia tenacissima (Roxb.) Moon (as A. tenacissima Roxb.)
• Matelea maritima (Jacq.) Woodson (as A. maritima Jacq.)
• Sarcostemma acidum (Roxb.) Voigt (as A. acida Roxb.)
• Sarcostemma viminale (L.) R.Br. (as A. viminalis (L.) Steud.)
• Telosma cordata (Burm.f.) Merr. (as A. cordata Burm.f.)
• Telosma pallida (Roxb.) Craib (as A. pallida Roxb.)
• Tylophora indica (Burm.f.) Merr. (as A. asthmatica L.f.)
• Vincetoxicum hirundinaria Medik. (as A. vincetoxicum L.)
• Vincetoxicum pycnostelma Kitag. (as A. paniculata Bunge)
• Xysmalobium undulatum (L.) R.Br. (as A. undulata L.)[31]

References

1. "Taxon: Asclepias L." Germplasm Resources Information Network. United States Department of Agriculture. 2003-03-13. Retrieved 2013-02-05.
2. "Asclepias". NCBI taxonomy. Bethesda, MD: National Center for Biotechnology Information. Retrieved 10 August 2018.
3. Singh, B.; Rastogi, R.P. (1970). "Cardenolides-glycosides and genins". Phytochemistry. 9 (2): 315–331. doi:10.1016/s0031-9422(00)85141-9.
4. Agrawal, Anurag (2017-03-07). Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and Their Remarkable Story of Coevolution. Princeton University Press. ISBN 9781400884766.
5. Agrawal, Anurag A.; Petschenka, Georg; Bingham, Robin A.; Weber, Marjorie G.; Rasmann, Sergio (2012-04-01). "Toxic cardenolides: chemical ecology and coevolution of specialized plant–herbivore interactions". New Phytologist. 194 (1): 28–45. doi:10.1111/j.1469-8137.2011.04049.x. ISSN 1469-8137. PMID 22292897.
6. "Asclepias L." Plants of the World Online. Royal Botanical Gardens Kew. Retrieved 2018-11-23.
7. "Asclepias". ipni.org. International Plant Names Index. Retrieved 2018-11-23.
8. Quattrocchi, Umberto (29 November 1999). CRC World Dictionary of Plant Names: Common Names, Scientific Names, Eponyms, Synonyms, and Etymology. CRC Press. p. 211. ISBN 978-0-8493-2673-8. Latin asclepias and Greek asklepias for the common swallowwort; Asclepius, Greek god of medicine, the worship of Asclepius was centered in Epidaurus. See W.K.C. Guthrie, The Greeks and Their Gods, 1950; Carl Linnaeus, Species Plantarum. 214. 1753 and Genera Plantarum. Ed. 5. 102. 1754.
9. http://orbisec.com/milkweed-flower-morphology-and-terminology/ Milkweed Flower Morphology
10. Robertson, C. (1887) Insect relations of certain asclepiads. I. Botanical Gazette 12: 207–216
11. Ollerton, J. & S. Liede. 1997. Pollination systems in the Asclepiadaceae: a survey and preliminary analysis. Biological Journal of the Linnean Society (1997), 62: 593–610.
12. Sacchi, C.F. (1987) Variability in dispersal ability of Common Milkweed, Asclepias syriaca, seeds, Oikos Vol. 49, pp. 191–198
13. Frost, S.W. (1965). "Insects and pollinia". Ecology. 46 (4): 556–558. doi:10.2307/1934896. JSTOR 1934896.
14. Ramanujan, Krishna (Winter 2008). "Discoveries: Milkweed evolves to shrug off predation". Northern Woodlands. 15 (4): 56.
15. Agrawal, Anurag A.; Fishbein, Mark (2008-07-22). "Phylogenetic escalation and decline of plant defense strategies". Proceedings of the National Academy of Sciences. 105 (29): 10057–10060. doi:10.1073/pnas.0802368105. ISSN 0027-8424. PMC 2481309. PMID 18645183.
16. Johnson, Glen A (2019). Milkweed of the United States including Puerto Rico and the US Virgin Islands. Amazon KDP. p. 7. ISBN 9781081170653.
17. Hauswirth, Katherine (2008-10-26). "The Heroic Milkweed". The Christian Science Monitor. Retrieved 2014-02-14.
18. Wykes, Gerald (2014-02-04). "A Weed Goes to War, and Michigan Provides the Ammunition". MLive Media Group. Michigan History Magazine. Retrieved 2014-02-14.
19. Evangelista, R.L. (2007). "Milkweed seed wing removal to improve oil extraction". Industrial Crops and Products. 25 (2): 210–217. doi:10.1016/j.indcrop.2006.10.002.
20. Bernstein, Jaela (2016-10-13). "How a Quebec company used a weed to create a one-of-a-kind winter coat". CBC News. Retrieved 2018-01-05.
21. McCullough, Elizabeth A. (April 1991). "Evaluation of Milkweed Floss as an Insulative Fill Material". Textile Research Journal. 61 (4): 203–210. doi:10.1177/004051759106100403.
22. "Milkweed touted as oil-spill super-sucker — with butterfly benefits". cbc.ca. 2 December 2014.
23. Charles Sigisbert, Sonnini (1810). Traité de l'asclépiade.
24. Choi, Hyung Min; Cloud, Rinn M. (1992). "Natural sorbents in oil spill cleanup". Environmental Science & Technology. 26 (4): 772. doi:10.1021/es00028a016.
25. "La soie d'Amérique passe en production industrielle". Radio Canada. Retrieved 20 December 2015.
26. (1) "Butterfly Gardening: Introduction". University of Kansas: Monarch Watch. Archived from the original on 2 February 2020. Retrieved 9 March 2020.
    (2) "Monarch Watch: Monarch Waystation Program". University of Kansas, Entomology Department. Archived from the original on 18 Nov 2019. Retrieved 26 February 2019.
    (3) "Monarch Garden Plants" (PDF). San Francisco, California: Pollinator Partnership. Archived from the original (PDF) on 9 March 2020. Retrieved 9 March 2020.
27. Howard, Elizabeth; Aschen, Harlen; Davis, Andrew K. (2010). "Citizen Science Observations of Monarch Butterfly Overwintering in the Southern United States". Psyche: A Journal of Entomology. 2010: 1. doi:10.1155/2010/689301.
28. Satterfield, D. A.; Maerz, J. C.; Altizer, S (2015). "Loss of migratory behaviour increases infection risk for a butterfly host". Proceedings of the Royal Society B: Biological Sciences. 282 (1801): 20141734. doi:10.1098/rspb.2014.1734. PMC 4308991. PMID 25589600.
29. Majewska, Ania A.; Altizer, Sonia (16 August 2019). "Exposure to Non-Native Tropical Milkweed Promotes Reproductive Development in Migratory Monarch Butterflies". Insects. 10 (8): 253. doi:10.3390/insects10080253. PMC 6724006. PMID 31426310.
30. Asclepias subverticillata (A. Gray) Vail, USDA PLANTS
31. "GRIN Species Records of Asclepias". Germplasm Resources Information Network. United States Department of Agriculture. Retrieved 2011-02-22.

• Everitt, J.H.; Lonard, R.L.; Little, C.R. (2007). Weeds in South Texas and Northern Mexico. Lubbock: Texas Tech University Press. ISBN 0-89672-614-2

External links

• Medical research
• Milkweed test-cultivated for the insulation value of floss
• Milkweed in Handbook of Energy Crops
• Common milkweed production research at Western Illinois University
• UVSC Herbarium — Asclepias