Asclepias

Title: Asclepias
Additional Names: Pleurisy root; butterfly weed
Literature References: Dried root of Asclepias tuberosa L., Asclepiadaceae. Habit. Ontario to Minnesota. Constit. Asclepiadin, resins, volatile oil.
Ascorbic Acid Ascorbigen Asiaticoside Asoprisnil Asoxime Chloride

Asclepias
Asclepias syriaca showing flowers and latex.
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Gentianales
Family: Apocynaceae
Subfamily: Asclepiadoideae
Tribe: Asclepiadeae
Subtribe: Asclepiadinae
Genus: Asclepias
L.[1]
Type species
Asclepias syriaca
L.
Species

See text.

Synonyms[1]
  • Acerates Elliott
  • Anantherix Nutt.
  • Asclepiodella Small
  • Asclepiodora A.Gray
  • Biventraria Small
  • Oxypteryx Greene
  • Podostemma Greene
  • Podostigma Elliott (probable)
  • Schizonotus A.Gray
  • Solanoa Greene
  • Trachycalymma (K.Schum.) Bullock (possible)
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 consists of a latex containing alkaloids 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 pappi, are blown by the wind. They have many different flower colorations.