Asclepias

"Milkweed" redirects here. For other uses, see Milkweed (disambiguation).
Asclepias
Asclepias syriaca showing flowers and latex.
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Gentianales
Family: Apocynaceae
Subfamily: Asclepiadoideae
Tribe: Asclepiadeae
Subtribe: Asclepiadinae
Genus: Asclepias
L.[1]
Type species
Asclepias syriaca
L.
Species

See text.

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)
Asclepias syriaca seed pods, Baldwinsville, New York
Milkweed sprout, a few days after sowing
Chemical structure of oleandrin, one of the cardiac glycosides

Asclepias L. (1753), the milkweeds, is an American genus of herbaceous perennial, dicotyledonous plants that contains over 140 known species. It previously belonged to the family Asclepiadaceae, but this is now classified as the subfamily Asclepiadoideae of the dogbane family Apocynaceae.

Milkweed is named for its milky sap, which consists of a latex containing alkaloids and several other complex compounds including cardenolides.[2] Some species are known to be toxic.

Carl Linnaeus named the genus after Asclepius, the Greek god of healing.[3]

Milkweed flowers

Asclepias species 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 filamens and styles) surrounded by a five-membered corona. The corona is composed of a five paired hood and horn structures 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.[4]

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).[5] Pollination is effected by the reverse procedure, in which one of the pollinia becomes trapped within the anther slit.

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

Asclepias species produce their seeds in follicles. The seeds, which are arranged in overlapping rows, bear a cluster of white, silky, filament-like hairs known as the coma[6] (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.

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,[5][7] and a 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.

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 more recently evolved milkweed species use these preventative strategies less but grow faster than older species, potentially regrowing faster than caterpillars can consume them.[8]

Uses

The milkweed filaments from the coma (the "floss") are hollow and coated with wax, and have good insulation qualities. During World War II, over 5,000 t (5,500 short tons) of milkweed floss were collected in the United States as a substitute for kapok.[9][10] As of 2007, milkweed is grown commercially as a hypoallergenic filling for pillows.[11] A study of the insulative properties of various materials found that milkweed floss was outperformed by other materials in insulation, loft, and lumpiness, but scored well on various metrics when mixed with down feathers.[12] Milkweed fibers are used to clean up oil spills.[13]

Seeds

In the past, the high dextrose content of the nectar led to milkweed's use as a source of sweetener for Native Americans and voyageurs.

The bast fibers of some species can be used for cordage.

Milkweed latex contains about 1 to 2% latex, and was attempted as a source of natural rubber by both Germany and the United States during World War II. No record has been found of large-scale success.

Grown commercially since 2012, particularly in Quebec, Asclepias is also known as "Silk of America" using a term "silk[14]" attributed by the naturalist Charles Sigisbert Sonnini that was brought into France as an exotic plant and a silk to be included in fabrics. Silk of America is a strand of common milkweed (Asclepias syriaca) gathered mainly in the valley of the Saint Lawrence River in Canada. The silk is used to manufacture thermal insulation, acoustic insulation and oil absorbents.[15][16]

Milkweed is beneficial to nearby plants, repelling some pests, especially wireworms.

Milkweed also contains cardiac glycoside poisons that inhibit animal cells from maintaining a proper K+, Ca+ concentration gradient. As a result, many natives 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 10% of their body weight in any part of the plant. Milkweed also causes mild dermatitis in some who come in contact with it.

The leaves of Asclepias species, and of some species formerly classified as Asclepias such as Gomphocarpus physocarpus, are the only food source for monarch butterfly larvae and other milkweed butterflies. These plants are therefore often used in butterfly gardening.

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' 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 humistrata Sandhill milkweed, native to southeastern United States
Asclepias incarnata Swamp milkweed, native to wetlands of North America
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 longifolia Longleaf milkweed
Asclepias meadii Mead's milkweed, native to midwestern United States
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[17]
Asclepias sullivantii Sullivant's milkweed
Asclepias syriaca Common 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

Formerly placed here

Some species formerly classified under the Asclepias genus include:

References

  1. 1 2 "Taxon: Asclepias L.". Germplasm Resources Information Network. United States Department of Agriculture. 2003-03-13. Retrieved 2013-02-05.
  2. ↑ Singh, B. and Rastogi, R.P. (1970). Cardenolides-glycosides and genins. Phytochemistry 9: 315-331.
  3. ↑ 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.
  4. ↑ http://orbisec.com/milkweed-flower-morphology-and-terminology/ Milkweed Flower Morphology
  5. 1 2 Robertson, C. (1887) Insect relations of certain asclepiads. I. Botanical Gazette 12: 207–216
  6. ↑ Sacchi, C.F. (1987) Variability in dispersal ability of Common Milkweed, Asclepias syriaca, seeds, Oikos Vol. 49, pp. 191-198
  7. ↑ Frost, S.W. (1965) Insects and pollinia. Ecology 46: 556–558
  8. ↑ Ramanujan, Krishna (Winter 2008). "Discoveries: Milkweed evolves to shrug off predation". Northern Woodlands. Center for Northern Woodlands Education. 15 (4): 56.
  9. ↑ Hauswirth, Katherine (2008-10-26). "The Heroic Milkweed". The Christian Science Monitor. Retrieved 2014-02-14.
  10. ↑ 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.
  11. ↑ 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.
  12. ↑ 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.
  13. ↑ "Milkweed touted as oil-spill super-sucker — with butterfly benefits". cbc.ca. 2 December 2014.
  14. ↑ Charles Sigisbert, Sonnini. Traité de l'asclépiade.
  15. ↑ "Natural sorbents in oil spill cleanup". ACS.
  16. ↑ "La soie d'Amérique passe en production industrielle". Radio Canada. Retrieved 20 December 2015.
  17. ↑ Asclepias subverticillata (A. Gray) Vail, USDA PLANTS
  18. ↑ "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

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