Milkweed

The milkweeds, Asclepias (L. 1753), are a genus of herbaceous perennial, dicotyledonous plants  that contains over 140 known species.

Milkweeds are an important nectar source for bees and other nectar eaters, and a food source for caterpillars. The weeds are eaten by caterpillars of the monarch butterfly and its relatives, and by other herbivorous insects (such as beetles, and true bugs). These insects are able to feed on the plants despite their chemical defences. Milkweed is named after its milky sap, which contains alkaloids, latex, and several other complex compounds. Some species are toxic.

Pollination in this genus is accomplished in an unusual manner, as the pollen is grouped into pollen sacs. 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.

Milkweeds have three defenses to limit damage by caterpillars and other insects: hairs on the leaves, toxins, and latex fluids. Some more recent milkweed species grow faster than older species. They have the potential to grow faster than  caterpillars can eat them. Caterpillars which eat milkweeds, and their adult butterflies, may be protected by the foul taste of the milkweed chemicals. Such butterflies and caterpillars usually show warning colors (see mimicry#warning coloration).

Species
 Asclepias albicans
 Asclepias amplexicaulis
 Asclepias asperula
 Asclepias californica
 Asclepias cordifolia
 Asclepias cryptoceras
 Asclepias curassavica
 Asclepias eriocarpa
 Asclepias erosa
 Asclepias exaltata
 Asclepias fascicularis
 Asclepias fruticosa
 Asclepias humistrata
 Asclepias incarnata
 Asclepias lanceolata
 Asclepias linaria
 Asclepias linearis

 Asclepias meadii
 Asclepias nyctaginifolia
 Asclepias obovata
 Asclepias physocarpa
 Asclepias purpurascens
 Asclepias quadrifolia
 Asclepias rubra
 Asclepias solanoana
 Asclepias speciosa
 Asclepias subulata
 Asclepias sullivantii
 Asclepias syriaca
 Asclepias tuberosa
 Asclepias variegata
 Asclepias verticillata
 Asclepias vestita
 Asclepias vincetoxicum
 Asclepias viridiflora

 References