''Asclepias'' is a
genus of herbaceous,
perennial,
flowering plants known as milkweeds, named for their
latex, a milky substance containing
cardiac glycosides termed
cardenolides, exuded where cells are damaged.
Most species are
toxic 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, 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 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 of the dogbane family,
Apocynaceae.
The genus was formally described by
Carl Linnaeus in 1753,
who named it after
Asclepius, the Greek god of healing.
Flowers
Members of the genus produce some of the most complex flowers in the plant kingdom, comparable to
orchids in complexity. Five petals reflex backwards revealing a
gynostegium surrounded by a five-membrane
corona. 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 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 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 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. 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''
(L.) W.T.Aiton (as ''A. gigantea''
L.)
* ''
Calotropis procera''
(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
''Cynanchum'' is a genus of about 300 species including some swallowworts, belonging to the family Apocynaceae. The taxon name comes from Greek ''kynos'' (meaning "dog") and ''anchein'' ("to choke"), hence the common name for several species is ...
''
(Freyn) K.Schum. (as ''A. sibirica''
L.)
* ''
Funastrum clausum
''Funastrum clausum'', commonly known as white twinevine, is a species of flowering plant in the Apocynum, dogbane family, Apocynaceae. It is native to southern Florida and Texas in the United States, Mexico, the Caribbean, Central America and So ...
''
(Jacq.) Schltr. (as ''A. clausa''
Jacq.)
* ''
Gomphocarpus cancellatus
''Gomphocarpus'' is a genus of plants in the 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 dogban ...
''
(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
''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, Afri ...
''
(Humb. & Bonpl. ex Willd.) E.Fourn. (as ''A. macrophylla''
Humb. & Bonpl. ex Schult.)
* ''
Marsdenia tenacissima''
(Roxb.) Moon (as ''A. tenacissima''
Roxb.)
* ''
Matelea maritima
''Matelea'' is a genus of flowering plants in the family Apocynaceae. It contains about 200 species, which are commonly known as milkvines. Some people consider '' Chthamalia'' to be a synonym to or a subgenus of ''Matelea''.
Selected species
...
''
(Jacq.) Woodson (as ''A. maritima''
Jacq.)
* ''
Sarcostemma acidum
''Cynanchum acidum'' is a species of flowering plant in the family Apocynaceae, typically found in the arid parts of peninsular India where it is used in religious sacrifices. The plant is religiously linked to Hinduism and is believed to be a m ...
''
(Roxb.) Voigt (as ''A. acida''
Roxb.)
* ''
Sarcostemma viminale
''Cynanchum viminale'' is a leafless succulent plant in the family Apocynaceae. The species is native to West Africa, the Indian Ocean and Western Pacific region. The species' natural range extends from South Africa throughout much of Africa and ...
''
(L.) R.Br. (as ''A. viminalis''
(L.) Steud.)
* ''
Telosma cordata
''Telosma cordata'' is a species of flowering plant, native to China () and Indo-China, in the family Apocynaceae (tribe Marsdenieae). It is cultivated elsewhere and may occur wild as an introduced species. Common names include Chinese violet, c ...
''
(Burm.f.) Merr. (as ''A. cordata''
Burm.f.)
* ''
Telosma pallida
''Telosma'' is a genus of plants in the family Apocynaceae, first described in 1905. It is native to Africa, and Asia.Gibbs Russell, G. E., W. G. M. Welman, E. Retief, K. L. Immelman, G. Germishuizen, B. J. Pienaar, M. Van Wyk & A. Nicholas. 1987 ...
''
(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
''Vincetoxicum'' is a genus of plants in the family Apocynaceae. Although the species in ''Vincetoxicum'' have sometimes been included in ''Cynanchum'', chemical and molecular evidence shows that ''Vincetoxicum'' is more closely related to ''Tylo ...
''
Kitag. (as ''A. paniculata''
Bunge)
* ''
Xysmalobium undulatum
''Xysmalobium'' is a genus of plants in the family Apocynaceae, first described as a genus in 1810. It is native to Africa.Brown, Robert. 1810. On the Asclepiadeae 27
;Species
;formerly included
moved to other genera ''(Asclepias, Glossostelm ...
''
(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
bee
Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyly, monophyletic lineage within the ...
s,
wasps, and other nectar-seeking insects, though non-native
honey bees commonly get trapped in the stigmatic slits and die.
Milkweeds are also the 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
Chemical defense is a life history strategy employed by many organisms to avoid consumption by producing toxic or repellent metabolites or chemical warnings which incite defensive behavioral changes. The production of defensive chemicals occurs in ...
.
Milkweeds use three primary
defenses to limit damage caused by caterpillars: hairs on the leaves (
trichomes),
cardenolide toxins, and
latex 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 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
''Ophryocystis elektroscirrha'' (sometimes abbreviated OE or ''O.e.'') is an obligate, neogregarine protozoan parasite that infects monarch (''Danaus plexippus'') and queen (''Danaus gilippus'') butterflies. There are no other known hosts. The s ...
'' (OE) parasite on the monarch butterfly, ''
Danaus plexippus''. The OE parasite causes holes to form in the wings of fully developed monarch butterflies,
Danaus plexippus, 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 fascicularis'' is a species of milkweed known by the common names narrowleaf milkweed and Mexican whorled milkweed. It is a perennial herb that grows in a variety of habitats.
Description
''Asclepias fascicularis'' is a flowering pe ...
'', ''
Asclepias tuberosa'', and ''Asclepias angustifolia''.
Monarch butterfly conservation and milkweeds
The leaves of ''Asclepias'' species are a food source for
monarch butterfly
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. It ...
larvae and some other
milkweed butterflies.
These plants are often used in
butterfly gardening 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 and
Central America. Year-round plantings of this species in the
United States 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
''Ophryocystis elektroscirrha'' (sometimes abbreviated OE or ''O.e.'') is an obligate, neogregarine protozoan parasite that infects monarch (''Danaus plexippus'') and queen (''Danaus gilippus'') butterflies. There are no other known hosts. The s ...
''. 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 fibers of some species can be used for rope. The
Miwok 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, more than of milkweed floss was collected in the US as a substitute for
kapok. Milkweed is grown commercially as a
hypoallergenic 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 in Canada. The silk is used in thermal insulation, acoustic insulation, and oil absorbents.
Milkweed
latex contains about two percent latex, and during World War II both
Nazi Germany and the US attempted to use it as a source of
natural rubber, although no record of large-scale success has been found.
Many milkweed species also contains
cardiac glycoside 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 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