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Humans have long used milkweeds as ornamental flowers, medicine, fabric, fragrance, even food.
Because of the monarch butterfly, with its extraordinary, long-distance winter migration, milkweed-the obligate food plant on which monarchs depend from hatchlings through pupation-has risen from insignificance to prominence. Common milkweed, Asclepias syriaca, is only one of over 100 species of Asclepias in North, Central, and South America, some of which are abundant and familiar. Each region of the United States and Mexico has one or more species, such as swamp milkweed, Asclepias incarnata, with white or pink blossoms, always near or in water. Butterfly weed, Asclepias tuberosa, is familiar in the Midwest and upper south. Further south into Texas and west into Arizona, the abundantly flowered antelope horns, Asclepias asperula capricornu, takes over pastures and hillsides, while in New Mexico, Colorado, and northward, there is showy milkweed, Asclepias speciosa. In desert washes and canyons of California, rush milkweed, Asclepias subulata, hides, while Indian or woollypod milkweed, Asclepias eriocarpa, grows inconspicuously in dry fields. These are just a few of the Asclepias species in North America.
There are other species that are so rare, or inaccessible, that they are known only to a few botanists. Conversely, tropical milkweed, Asclepias curassavica, has become a prominent plant in the nursery trade, and hence, in home gardens. It has been planted around the world and is becoming an invasive pest in the gardens and waste areas of some regions. It is now known in temperate parts of Australia, Africa, and Asia. Local species of butterflies, as well as moths, true bugs, even grasshoppers have adapted to the plant while using their native milkweeds mostly for larval host plants. It should be noted that the blossoms of most Asclepias species, including tropical milkweed, are favorites of honeybees and other insects for nectar and pollen.
Ordinarily, when we speak of milkweed we are speaking of Asclepias, the genus of a large, complex family that includes such garden plants as plumeria, oleander, and allamanda. The genus is one of many members of a large subfamily that carries its name: Asclepiadoideae, which is itself part of the dog bane family, Apocynaceae. But there are many kinds of milkweed. There are vines, some luxuriant in leaf growth and flowering umbels,...