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Milkweed

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Milkweed

"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 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. As of 2007, milkweed is grown commercially as a hypoallergenic filling for pillows.[3] 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.[4]


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. 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.

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 Whitestem milkweed
Asclepias amplexicaulis Blunt-leaved milkweed
Asclepias asperula Antelope horns
Asclepias californica California milkweed
Asclepias cordifolia Heart-leaf milkweed
Asclepias cryptoceras Pallid milkweed
Asclepias curassavica Scarlet milkweed, tropical milkweed, bloodroot, bloodflower, bastard ipecacuanha
Asclepias eriocarpa Woollypod milkweed
Asclepias erosa Desert milkweed
Asclepias exaltata Poke milkweed
Asclepias fascicularis Narrow-leaf milkweed
Asclepias fruticosa syn. Gomphocarpus fruticosus Swan plant, African milkweed
Asclepias humistrata Sandhill milkweed
Asclepias incarnata Swamp milkweed
Asclepias lanceolata Lanceolate milkweed (Cedar Hill milkweed)
Asclepias linaria Pine needle milkweed
Asclepias linearis Slim milkweed
Asclepias longifolia Longleaf milkweed
Asclepias meadii Mead's milkweed
Asclepias nyctaginifolia Mojave milkweed
Asclepias obovata Pineland milkweed
Asclepias physocarpa Balloonplant, balloon cotton-bush, giant swan plant, swan plant
Asclepias purpurascens Purple milkweed
Asclepias quadrifolia Four-leaved milkweed
Asclepias rubra Red milkweed
Asclepias solanoana Serpentine milkweed
Asclepias speciosa Showy milkweed
Asclepias subulata Rush milkweed, leafless milkweed
Asclepias subverticillata Horsetail milkweed[5]
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
Asclepias viridis Green milkweed
Asclepias welshii Welsh's milkweed

Formerly placed here

Some species formerly classified under the Asclepias genus 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.)[6]

References

External links

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