Asclepias

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

Asclepias
Asclepias syriaca showing flowers and latex like sap.
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Gentianales
Family:	Apocynaceae
Subfamily:	Asclepiadoideae
Tribe:	Asclepiadeae
Subtribe:	Asclepiadinae
Genus:	Asclepias L.
Type species
Asclepias syriaca L.
Species
See text.
Synonyms
Acerates Elliott Anantherix Nutt. Asclepiodella Small Asclepiodora A.Gray Biventraria Small Oxypteryx Greene Podostemma Greene Schizonotus A.Gray Solanoa Greene

Asclepias syriaca seed pods, Baldwinsville, New York

A species of Mexican milkweed - note the specialized flower structure

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 contains alkaloids, latex, 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 pappus, 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.

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
	Asclepias linaria	Pine needle milkweed
	Asclepias linearis	Slim 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	Poison milkweed
	Asclepias sullivantii	Sullivant's milkweed
	Asclepias syriaca	Common milkweed
	Asclepias tuberosa	Indian Paintbrush, Butterfly weed, Pleurisy root
	Asclepias variegata	White milkweed
	Asclepias verticillata	Whorled milkweed
	Asclepias vestita	Woolly milkweed
	Asclepias vincetoxicum
	Asclepias viridiflora
	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.)

Uses

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 5,000 t (5,500 short tons) of milkweed floss was collected in the United States as a substitute for kapok. As of 2007, milkweed is grown commercially as a hypoallergenic filling for pillows.

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% 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 a common folk remedy used for the clotting of small wounds and the removal of 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.^{[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.

Milkweed sap is also externally used as a natural remedy for poison ivy.

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

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

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
• Milkweed Photo Gallery