Asclepias L. (1753), the milkweeds, is a genus of herbaceous perennial, dicotyledonous plants that contains over 140 known species. It used to belong 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.
Pollination in this genus is accomplished in an unusual manner, as the pollen is grouped into complex structures called pollinia (or "pollen sacs"), rather than being individual grains, as is typical for plant pollen. The flower petals are smooth and rigid, and the feet of visiting insects (predominantly large wasps, such as spider wasps, which visit the plants for nectar) slip into notches in the flowers, where the sticky bases of the pollinia attach to the feet, pulling the pollen sacs free when the pollinator flies off. Bees, including honey bees only gather nectar from milkweed flowers, and are generally not effective pollinators despite the frequency of visitation.
Species in the Asclepias genus grow their seeds in pods. These seed pods contain soft filaments known as either silk or floss. The filaments are attached to individual seeds. When the seed pod ripens, the seeds are blown by the wind, each carried by several filaments.
|Asclepias acida||Possibly used to create Soma.|
|Asclepias amplexicaulis||Blunt-leaved milkweed|
|Asclepias asperula||Antelope horns|
|Asclepias cordifolia||Heart-leaf milkweed|
|Asclepias curassavica||Scarlet milkweed, Bloodroot, Bastard Ipecacuanha|
|Asclepias exaltata||Poke milkweed|
|Asclepias fascicularis||Narrow leaf milkweed|
|Asclepias humistrata||Sandhill milkweed|
|Asclepias incarnata||Swamp milkweed|
|Asclepias lanceolata||Lanceolate milkweed|
|Asclepias physocarpa||Gomphocarpus physocarpus, commonly balloonplant, balloon cotton-bush or swan plant|
|Asclepias purpurascens||Purple milkweed|
|Asclepias quadrifolia||Four-leaved milkweed|
|Asclepias rubra||Red milkweed|
|Asclepias speciosa||Showy milkweed|
|Asclepias subulata||Rush milkweed(Leafless milkweed)|
|Asclepias sullivantii||Sullivant's milkweed|
|Asclepias syriaca||Common milkweed|
|Asclepias tuberosa||Butterfly weed, Pleurisy root|
|Asclepias variegata||White milkweed|
|Asclepias verticillata||Whorled milkweed|
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 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. Fatality is possible when animal consumes 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.