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''Asclepias'' is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of herbaceous,
perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...
,
flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...
s known as milkweeds, named for their
latex Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well. In nature, latex is found as a milky fluid found in 10% of all flowering plants (angiosperms ...
, a milky substance containing
cardiac glycoside Cardiac glycosides are a class of organic compounds that increase the output force of the heart and decrease its rate of contractions by inhibiting the cellular sodium-potassium ATPase pump. Their beneficial medical uses are as treatments for c ...
s termed
cardenolide A cardenolide is a type of steroid. Many plants contain derivatives, collectively known as cardenolides, including many in the form of cardenolide glycosides (cardenolides that contain structural groups derived from sugars). Cardenolide glycoside ...
s, exuded where cells are damaged. Most species are
toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...
to humans and many other species, primarily due to the presence of cardenolides, although, as with many such plants, there are species that feed upon them (e.g. their leaves) and from them (e.g. their nectar). Most notable are
monarch butterflies The monarch butterfly or simply monarch (''Danaus plexippus'') is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown. ...
, who use and require certain milkweeds as host plants for their
larvae A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...
. The genus contains over 200 species distributed broadly across Africa, North America, and South America. It previously belonged to the
family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
Asclepiadaceae, which is now classified as the
subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...
Asclepiadoideae The Asclepiadoideae are a subfamily of plants in the family Apocynaceae. Formerly, they were treated as a separate family under the name Asclepiadaceae, e.g. by APG II, and known as the milkweed family. They form a group of perennial herbs, twin ...
of the dogbane family,
Apocynaceae Apocynaceae (from ''Apocynum'', Greek for "dog-away") is a family of flowering plants that includes trees, shrubs, herbs, stem succulents, and vines, commonly known as the dogbane family, because some taxa were used as dog poison Members of ...
. The genus was formally described by
Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
in 1753, who named it after
Asclepius Asclepius (; grc-gre, Ἀσκληπιός ''Asklēpiós'' ; la, Aesculapius) is a hero and god of medicine in ancient Religion in ancient Greece, Greek religion and Greek mythology, mythology. He is the son of Apollo and Coronis (lover of ...
, the Greek god of healing.


Flowers

Members of the genus produce some of the most complex flowers in the plant kingdom, comparable to
orchids Orchids are plants that belong to the family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Along with the Asteraceae, they are one of the two largest families of flowering ...
in complexity. Five petals reflex backwards revealing a gynostegium surrounded by a five-membrane
corona Corona (from the Latin for 'crown') most commonly refers to: * Stellar corona, the outer atmosphere of the Sun or another star * Corona (beer), a Mexican beer * Corona, informal term for the coronavirus SARS-CoV-2, which causes the COVID-19 di ...
. The corona is composed of a five-paired hood-and-horn structure 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''.
Pollination Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds ...
in this genus is accomplished in an unusual manner. Pollen is grouped into complex structures called
pollinia A pollinium (plural pollinia) is a coherent mass of pollen grains in a plant that are the product of only one anther, but are transferred, during pollination, as a single unit. This is regularly seen in plants such as orchids and many species of mil ...
(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 stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filam ...
. 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).Robertson, C. (1887) Insect relations of certain asclepiads. I. Botanical Gazette 12: 207–216 Pollination is effected by the reverse procedure, in which one of the pollinia becomes trapped within the anther slit. Large-bodied
hymenoptera Hymenoptera is a large order (biology), order of insects, comprising the sawfly, sawflies, wasps, bees, and ants. Over 150,000 living species of Hymenoptera have been described, in addition to over 2,000 extinct ones. Many of the species are Par ...
ns (bees, wasps) are the most common and best pollinators, accounting for over 50% of all ''Asclepias'' pollination, whereas
monarch butterflies The monarch butterfly or simply monarch (''Danaus plexippus'') is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown. ...
are poor pollinators of milkweed. ''Asclepias'' species produce their seeds in pods termed follicles. The seeds, which are arranged in overlapping rows, bear a cluster of white, silky, filament-like hairs known as the coma (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 Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...
. Some, but not all, milkweeds also reproduce by clonal (or vegetative) reproduction.


Selected species

There are also 12 species of ''Asclepias'' in South America, among them: '' A. barjoniifolia'', '' A. boliviensis'', '' A. curassavica'', '' A. mellodora'', '' A. candida'', '' A. flava'', and '' A. pilgeriana''.


Deprecated

* ''
Calotropis gigantea ''Calotropis gigantea'', the crown flower, is a species of ''Calotropis'' native to Cambodia, Vietnam, Bangladesh, Indonesia, Malaysia, Thailand, Sri Lanka, India, China, Pakistan, and Nepal. It is a large shrub growing to tall. It has clus ...
'' (L.) W.T.Aiton (as ''A. gigantea'' L.) * ''
Calotropis procera ''Calotropis procera'' is a species of flowering plant in the family Apocynaceae that is native to North Africa, Pakistan,tropical Africa, Western Asia, South Asia, and Indochina. The green fruits contain a toxic milky sap that is extremely bi ...
'' (Aiton) W.T.Aiton (as ''A. procera'' Aiton) * ''
Cynanchum louiseae ''Vincetoxicum nigrum'', a species in the family Apocynaceae, also known as black swallow-wort, Louise's swallow-wort, or black dog-strangling vine, is a species of plant that is native to Europe and is found primarily in Italy, France, Portugal, ...
'' Kartesz & Gandhi (as ''A. nigra'' L.) * '' Cynanchum thesioides'' (Freyn) K.Schum. (as ''A. sibirica'' L.) * ''
Funastrum clausum ''Funastrum clausum'', commonly known as white twinevine, is a species of flowering plant in the dogbane family, Apocynaceae. It is native to southern Florida and Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South ...
'' (Jacq.) Schltr. (as ''A. clausa'' Jacq.) * '' Gomphocarpus cancellatus'' (Burm.f.) Bruyns (as ''A. cancellatus'' Burm.f. or ''A. rotundifolia'' Mill.) * ''
Gomphocarpus fruticosus ''Gomphocarpus fruticosus'' is a species of plant native to South Africa. It is also common in New Zealand where it is the main host of the monarch butterfly. The plant's tissues contain sufficient cardenolides that consumption of significant qu ...
'' (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 ''Marsdenia'' is a genus of plants in the family Apocynaceae first described as a genus in 1810. It is named in honor of the plant collector and Secretary of the Admiralty, William Marsden. The plants are native to tropical regions in Asia, Afr ...
'' (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 ''Tylophora'' is a genus of climbing plant or vine, first described as a genus in 1810. It is native to tropical and subtropical Asia, Africa, and Australia. Most of the species are perennial lianas. The name is derived from the Ancient Greek ...
'' (Burm.f.) Merr. (as ''A. asthmatica'' L.f.) * ''
Vincetoxicum hirundinaria ''Vincetoxicum hirundinaria'', commonly named white swallow-wort, is a long-lived herbaceous perennial of the genus ''Vincetoxicum'' in the family Apocynaceae. Etymology The generic name ''Vincetoxicum'', in Latin meaning ‘conqueror of poisonâ ...
'' Medik. (as ''A. vincetoxicum'' L.) * '' Vincetoxicum pycnostelma'' Kitag. (as ''A. paniculata'' Bunge) * '' Xysmalobium undulatum'' (L.) R.Br. (as ''A. undulata'' L.)


Ecology

Milkweeds are an important
nectar Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists ...
source for native bees,
wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. Th ...
s, and other nectar-seeking insects, though non-native
honey bees A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current cosm ...
commonly get trapped in the stigmatic slits and die. Milkweeds are also the larval food source for
monarch butterflies The monarch butterfly or simply monarch (''Danaus plexippus'') is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown. ...
and their relatives, as well as a variety of other herbivorous insects (including numerous
beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...
s,
moth Moths are a paraphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of w ...
s, and
true bug Hemiptera (; ) is an order of insects, commonly called true bugs, comprising over 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from to around , ...
s) 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 (
trichome Trichomes (); ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a pla ...
s),
cardenolide A cardenolide is a type of steroid. Many plants contain derivatives, collectively known as cardenolides, including many in the form of cardenolide glycosides (cardenolides that contain structural groups derived from sugars). Cardenolide glycoside ...
toxins, and
latex Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well. In nature, latex is found as a milky fluid found in 10% of all flowering plants (angiosperms ...
fluids. Data from a DNA study indicate that, generally, more recently evolved milkweed species ("derived" in botany parlance) use these preventive strategies less but grow faster than older species, potentially regrowing faster than caterpillars can consume them. Research indicates that the very high
cardenolide A cardenolide is a type of steroid. Many plants contain derivatives, collectively known as cardenolides, including many in the form of cardenolide glycosides (cardenolides that contain structural groups derived from sugars). Cardenolide glycoside ...
content of ''
Asclepias linaria ''Asclepias linaria'' is a species of milkweed known by the common name pineneedle milkweed. It is native to the Mojave and Sonoran Deserts of Northwestern Mexico and the U.S. states of California and Arizona. This is a large erect perennial h ...
'' reduces the impact of the '' Ophryocystis elektroscirrha'' (OE) parasite on the monarch butterfly, ''
Danaus plexippus The monarch butterfly or simply monarch (''Danaus plexippus'') is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown. I ...
''. The OE parasite causes holes to form in the wings of fully developed monarch butterflies,
Danaus plexippus The monarch butterfly or simply monarch (''Danaus plexippus'') is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae. Other common names, depending on region, include milkweed, common tiger, wanderer, and black-veined brown. I ...
, this causes weakened endurance and an inability to migrate. The parasite only affects monarchs when they are larvae and caterpillars, but the detriment is when they are in their butterfly form. By contrast, some species of ''Asclepias'' are extremely poor sources of cardenolides, such as '' Asclepias fascicularis'', ''
Asclepias tuberosa ''Asclepias tuberosa'', commonly known as butterfly weed, is a species of milkweed native to eastern and southwestern North America. It is commonly known as butterfly weed because of the butterflies that are attracted to the plant by its color ...
'', and ''Asclepias angustifolia''.


Monarch butterfly conservation and milkweeds

The leaves of ''Asclepias'' species are a food source for monarch butterfly larvae and some other
milkweed butterflies Danainae is a subfamily of the family Nymphalidae, the brush-footed butterflies. It includes the Daniadae, or milkweed butterflies, who lay their eggs on various milkweeds on which their larvae (caterpillars) feed, as well as the clearwing butte ...
. These plants are often used in
butterfly gardening Butterfly gardening is a way to create, improve, and maintain habitat for lepidopterans including butterflies, skippers, and moths. Butterflies have four distinct life stages—egg, larva, chrysalis, and adult. In order to support and sustain ...
and monarch waystations in an effort to help increase the dwindling monarch population. However, some milkweed species are not suitable for butterfly gardens and monarch waystations. For example, '' A. curassavica'', or tropical milkweed, is often planted as an ornamental in butterfly gardens outside of its native range of
Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
and
Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
. Year-round plantings of this species in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
are controversial and criticised, as they may lead to new overwintering sites along the U.S. Gulf Coast and the consequent year-round breeding of monarchs. This is thought to adversely affect migration patterns, and to cause a dramatic build-up of the dangerous parasite, '' Ophryocystis elektroscirrha''. New research also has shown that monarch larvae reared on tropical milkweed show reduced migratory development (reproductive diapause), and when migratory adults are exposed to tropical milkweed, it stimulates reproductive tissue growth. Because of this, it is most often suggested to grow milkweeds that are native to the geographical area they are planted in to prevent negative impacts on monarch butterflies. Monarch caterpillars do not favor butterfly weed ('' A. tuberosa''), perhaps because the leaves of that milkweed species contain very little cardenolide. Some other milkweeds may have similar characteristics.


Uses

Milkweeds are not grown commercially in large scale, but the plants have had many uses throughout human history. Milkweeds have a long history of medicinal, every day, and military use. The Omaha people from Nebraska, the Menomin from Wisconsin and upper Michigan, the Dakota from Minnesota, and the Ponca people from Nebraska, traditionally used common milkweed ('' A. syriaca'') for medicinal purposes. The
bast fiber Bast fibre (also called phloem fibre or skin fibre) is plant fibre collected from the phloem (the "inner bark", sometimes called "skin") or bast surrounding the stem of certain dicotyledonous plants. It supports the conductive cells of the phlo ...
s of some species can be used for rope. The
Miwok The Miwok (also spelled Miwuk, Mi-Wuk, or Me-Wuk) are members of four linguistically related Native American groups indigenous to what is now Northern California, who traditionally spoke one of the Miwok languages in the Utian family. The word ...
people of northern California used heart-leaf milkweed ('' A. cordifolia'') for its stems, which they dried and used for cords, strings and ropes. A study of the insulative properties of various materials found that milkweed floss was outperformed by other materials in terms of insulation, loft, and lumpiness, but it scored well when mixed with down feathers. The milkweed filaments from the coma (the "floss") are hollow and coated with wax, and have good insulation qualities. During
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, more than of milkweed floss was collected in the US as a substitute for kapok. Milkweed is grown commercially as a
hypoallergenic Hypoallergenic, meaning "below average" or "slightly" allergenic, is a term meaning that something (usually cosmetics, pets, textiles, food, etc.) causes fewer allergic reactions. The term was first used in 1953 in an advertising campaign for cos ...
filling for pillows and as insulation for winter coats. ''Asclepias'' is also known as "Silk of America" which is a strand of common milkweed (''A. syriaca'') gathered mainly in the valley of the
Saint Lawrence River The St. Lawrence River (french: Fleuve Saint-Laurent, ) is a large river in the middle latitudes of North America. Its headwaters begin flowing from Lake Ontario in a (roughly) northeasterly direction, into the Gulf of St. Lawrence, connectin ...
in Canada. The silk is used in thermal insulation, acoustic insulation, and oil absorbents. Milkweed
latex Latex is an emulsion (stable dispersion) of polymer microparticles in water. Latexes are found in nature, but synthetic latexes are common as well. In nature, latex is found as a milky fluid found in 10% of all flowering plants (angiosperms ...
contains about two percent latex, and during World War II both
Nazi Germany Nazi Germany (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was ...
and the US attempted to use it as a source of
natural rubber Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, and ...
, although no record of large-scale success has been found. Many milkweed species also contains
cardiac glycoside Cardiac glycosides are a class of organic compounds that increase the output force of the heart and decrease its rate of contractions by inhibiting the cellular sodium-potassium ATPase pump. Their beneficial medical uses are as treatments for c ...
poisons that inhibit animal cells from maintaining a proper K+, Ca2+ concentration gradient. As a result, many peoples of South America and Africa used arrows poisoned with these glycosides to fight and hunt more effectively. Some milkweeds are toxic enough to cause death when animals consume large quantities of the plant. Some milkweeds also cause mild
dermatitis Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can v ...
in some who come in contact with them. Nonetheless, some species can be made edible if properly processed.


References

*


External links


Milkweed test-cultivated for the insulation value of floss




* ttps://web.archive.org/web/20070302042416/http://herbarium.uvsc.edu/Virtual/search.asp?s=genus&p=1&n=1386&t=Asclepias UVSC Herbarium — Asclepias {{Authority control Apocynaceae genera Butterfly food plants Taxa named by Carl Linnaeus Symbols of Illinois