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Milkweeds
Asclepias syriaca showing flowers and latex like sap.
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Gentianales
Family: Apocynaceae
Subfamily: Asclepiadoideae
Genus: Asclepias
L.
Type species
Asclepias syriaca L.
Species

See text.

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 a subfamily Asclepiadoideae of the dogbane family Apocynaceae.

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. Milkweed is named for its milky juice, which contains alkaloids, latex, and several other complex compounds including cardenolides. Some species are known to be toxic.

Carolus 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 if 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 pappus, are blown by the wind.

Milkweeds use three primary defenses to limit damage caused by caterpillars: hairs on the leaves, cardenolid toxins, and latex fluids. Data from a DNA study indicates that more recently evolved milkweed species utilize less of these preventative strategies, but grow faster than older species; potentially regrowing faster than caterpillars can consume them.[1]

Contents

Species

Some Asclepias species:

Asclepias albicans Whitestem milkweed
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
Asclepias cryptoceras Pallid milkweed
Asclepias curassavica crop.jpg Asclepias curassavica Scarlet milkweed, Tropical milkweed, Bloodroot, Bloodflower, Bastard Ipecacuanha
Asclepias eriocarpa Woollypod milkweed
Asclepias erosa 5.jpg Asclepias erosa Desert milkweed
Asclepias exaltata Poke milkweed
Asclepias fascicularis flowers 2003-06-05.jpg Asclepias fascicularis Narrow leaf milkweed
Asclepias fruticosa fruits.jpg Asclepias fruticosa syn. Gomphocarpus fruticosus swan plant, African milkweed
Asclepias humistrata Sandhill milkweed
Swamp Milkweed Asclepias incarnata Flowers Closeup 2800px.jpg Asclepias incarnata Swamp milkweed
Asclepias lanceolata Lanceolate milkweed
Asclepias linaria Pine needle milkweed
Asclepias linearis Slim milkweed
Asclepias meadii Mead's milkweed
Asclepias nyctaginifolia.jpg Asclepias nyctaginifolia Mojave milkweed
Asclepias obovata Pineland milkweed
Gomphocarpus physocarpus 1.jpg Asclepias physocarpa Gomphocarpus physocarpus, commonly balloonplant, balloon cotton-bush, giant swan plant, testicle tree, bishop's balls or swan plant
Purple Milkweed Asclepias purpurascens Head.jpg Asclepias purpurascens Purple milkweed
Asclepias quadrifolia Four-leaved milkweed
Asclepias rubra Red milkweed
Asclepiassolanoana.jpg 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 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 variegata White milkweed
Asclepias verticillata.jpg Asclepias verticillata Whorled milkweed
Asclepias vestita Woolly milkweed
Asclepias vincetoxicum
Asclepiasviridiflora.jpg Asclepias viridiflora

Uses

Asclepias syriaca seed pods
Baldwinsville, New York
A species of Mexican milkweed - note the specialized flower structure
Example of the chemical structure of one of the cardiac glycosides.

The milkweed filaments from the follicles are hollow and coated with wax, and have good insulation qualities. Tests have shown them to be superior to down feathers for insulation. During World War II, over 11 million pounds (5000 t) 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.[2]

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 were also used for cordage.

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

Milkweed is a common folk remedy used for removing warts. Milkweed sap is applied directly to the wart several times daily until the wart falls off. Dandelion sap is often used in the same manner.

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 1/10 its body weight in any part of the plant. Milkweed also causes mild dermatitis in some who come in contact with it.

Milkweed sap is also externally used as a natural remedy for Poison Ivy.

Being the sole food source of Monarch Butterfly larva, the plant is often used in Butterfly gardening.

See also

References

  • 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
  1. ^ Ramanujan, Krishna (Winter 2008). "Discoveries: Milkweed evolves to shrug off predation". Northern Woodlands (Center for Northern Woodlands Education) 15 (4): 56.  
  2. ^ 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  

External links


Simple English

Milkweeds
File:Purple Milkweed Asclepias purpurascens Feeding
Asclepias + ant feeding on nectar
Scientific classification
Kingdom: Plantae
(unranked) Eudicots
(unranked) Asterids
Order: Gentianales
Family: Apocynaceae
Subfamily: Asclepiadoideae
Genus: Asclepias
L.
Species

See text.

The milkweeds, Asclepias (L. 1753), are a genus of herbaceous perennial, dicotyledonous plants that contains over 140 known species.

Milkweeds are an important nectar source for bees and other nectar eaters, and a food source for caterpillars. The weeds are eaten by caterpillars of the monarch butterfly and its relatives, and by other herbivorous insects (such as beetles, and true bugs). These insects are able to feed on the plants despite their chemical defences. Milkweed is named after its milky sap, which contains alkaloids, latex, and several other complex compounds. Some species are toxic.

Pollination in this genus is accomplished in an unusual manner, as the pollen is grouped into pollen sacs. 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.

Milkweeds have three defenses to limit damage by caterpillars and other insects: hairs on the leaves, toxins, and latex fluids. Some more recent milkweed species grow faster than older species. They have the potential to grow faster than caterpillars can eat them.[1] Caterpillars which eat milkweeds, and their adult butterflies, may be protected by the foul taste of the milkweed chemicals. Such butterflies and caterpillars usually show warning colours (see mimicry#warning colouration).

Species

References

  1. Ramanujan, Krishna (Winter 2008). [Expression error: Unexpected < operator "Discoveries: Milkweed evolves to shrug off predation"]. Northern Woodlands (Center for Northern Woodlands Education) 15 (4): 56. 
  • 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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