Asclepias

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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.

Synonyms1
  • 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
A species of Mexican milkweed - note the specialized flower structure
A milkweed sprout, few days after sowing
Chemical structure of oleandrin, one of the cardiac glycosides

Asclepias L. (1753), the milkweeds, is a 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 juice which consists of a latex containing alkaloids and several other complex compounds including cardenolides. Some species are known to be toxic.

Carl Linnaeus named the genus after Asclepius, the Greek god of healing, because of the many folk-medicinal uses for the milkweed plants.

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, pulling a pair of pollen sacs free when the pollinator flies off. Pollination is effected by the reverse procedure in which one of the pollinia becomes trapped within the anther slit.

Asclepias species produce their seeds in follicles. The seeds, which are arranged in overlapping rows, have white, silky, filament-like hairs known as pappus, silk, or floss. The follicles ripen and split open, and the seeds, each carried by several dried pappi, are blown by the wind. They have many different flower colorations.

Ecology

Milkweeds are an important nectar source for bees and other nectar-seeking insects, 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 more recently evolved milkweed species use less of these preventative strategies, but grow faster than older species, potentially regrowing faster than caterpillars can consume them.2

Uses

The milkweed filaments from the follicles 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.34 As of 2007, milkweed is grown commercially as a hypoallergenic filling for pillows.5 A study of the insulative properties of various materials found that milkweed was outperformed by other materials in insulation, loft, and lumpiness, but scored well on various metrics when mixed with down feathers.6

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.

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

Milkweed also contains cardiac glycoside poisons which inhibit animal cells from maintaining a proper K+, Ca+ concentration gradient.citation needed 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.citation needed Milkweed also causes mild dermatitis in some who come in contact with it.

Being the sole food source of monarch butterfly larvae, the plant is often used in butterfly gardening.

In a garden, milkweed flowers will produce a strong and beautiful fragrance that will be as powerful as in any other flower.

Species

Some Asclepias species:

Asclepias-albicans.jpg Asclepias albicans Whitestem milkweed
Asclepias amplexicaulis.png Asclepias amplexicaulis Blunt-leaved milkweed
Asclepias asperula - Antelope Horns.jpg Asclepias asperula Antelope horns
Asclepias sp. flowers (Marshal Hedin).jpg Asclepias californica California milkweed
Asclepias cordifolia.JPG Asclepias cordifolia Heart-leaf milkweed
Asclepiascryptoceras.jpg Asclepias cryptoceras Pallid milkweed
Asclepias curassavica (Mexican Butterfly Weed) W IMG 1570.jpg Asclepias curassavica Scarlet milkweed, tropical milkweed, bloodroot,citation needed bloodflower, bastard ipecacuanha
Asclepiaseriocarpa.jpg Asclepias eriocarpa Woollypod milkweed
Asclepias erosa 5.jpg Asclepias erosa Desert milkweed
Asclepias exaltata (2985661678).jpg Asclepias exaltata Poke milkweed
Asclepias fascicularis flowers 2003-06-05.jpg Asclepias fascicularis Narrow-leaf milkweed
Asclepias humistrata.jpg Asclepias humistrata Sandhill milkweed
Swamp Milkweed Asclepias incarnata Flowers Closeup 2800px.jpg Asclepias incarnata Swamp milkweed
Asclepias lanceolata plant.jpg Asclepias lanceolata Lanceolate milkweed (Cedar Hill milkweed)
Asclepias linaria.jpg Asclepias linaria Pine needle milkweed
Asclepias linearis Slim milkweed
Asclepias longifolia.JPG Asclepias longifolia Longleaf milkweed
Asclepiasmeadii.jpg Asclepias meadii Mead's milkweed
Asclepias nyctaginifolia.jpg Asclepias nyctaginifolia Mojave milkweed
Asclepias obovata Pineland milkweed
Purple Milkweed Asclepias purpurascens Head.jpg Asclepias purpurascens Purple milkweed
Asclepias quadrifolia 001.jpg Asclepias quadrifolia Four-leaved milkweed
BB-3386 Asclepias rubra.png Asclepias rubra Red milkweed
Asclepias solanoana.jpeg Asclepias solanoana Serpentine milkweed
R27182818 milkweed img 0312.jpg Asclepias speciosa Showy milkweed
Asclepias subulata flowers 2.jpg Asclepias subulata Rush milkweed, leafless milkweed
Asclepias subverticillata.jpg Asclepias subverticillata Horsetail milkweed7
Asclepias sullivantii.jpg Asclepias sullivantii Sullivant's milkweed
Common milkweed-tracy.jpg Asclepias syriaca Common milkweed
Butterfly Weed Asclepias tuberosa Umbel.jpg Asclepias tuberosa Butterfly weed, pleurisy root
Asclepias uncialis lg.jpg Asclepias uncialis Wheel milkweed
Asclepias variegata.jpg Asclepias variegata White milkweed
Asclepias verticillata (3197723098).jpg Asclepias verticillata Whorled milkweed
Asclepias vestita Woolly milkweed
Asclepiasviridiflora.jpg Asclepias viridiflora
Asclepias viridis 1.jpg Asclepias viridis Green milkweed
Asclepias welshii 1.jpg Asclepias welshii Welsh's milkweed

Formerly placed here

Some species formerly classified under the Asclepias genus include:

References

  1. ^ a b "Taxon: Asclepias L.". Germplasm Resources Information Network. United States Department of Agriculture. 2003-03-13. Retrieved 2013-02-05. 
  2. ^ Ramanujan, Krishna (Winter 2008). "Discoveries: Milkweed evolves to shrug off predation". Northern Woodlands (Center for Northern Woodlands Education) 15 (4): 56. 
  3. ^ Hauswirth, Katherine (2008-10-26). "The Heroic Milkweed". The Christian Science Monitor. Retrieved 2014-02-14. 
  4. ^ 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. 
  5. ^ 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. 
  6. ^ McCullough, Elizabeth A. (April 1991). "Evaluation of Milkweed Floss as an Insulative Fill Material". Textile Research Journal 61 (4): 203–210. 
  7. ^ Asclepias subverticillata (A. Gray) Vail, USDA PLANTS
  8. ^ "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

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