Asclepias syriaca, commonly called common milkweed, butterfly flower, silkweed, silky swallow-wort, and Virginia silkweed, is a species of flowering plant. It is native to southern Canada and much of the United States east of the Rocky Mountains, excluding the drier parts of the prairies. It is in the genus Asclepias, the milkweeds. It grows in sandy soils as well as other kinds of soils in sunny areas. Description A. syriaca is a clonal perennial forb growing up to tall. Individual plants grow from rhizomes. All parts of common milkweed plants produce a white latex when cut. The simple leaves are opposite, sometimes whorled; broadly ovate-lanceolate. They grow to long and broad, usually with entire, undulate margins and reddish main veins. They have very short petioles and velvety undersides. The highly fragrant, nectariferous flowers vary from white (rarely) through pinkish and purplish and occur in umbellate cymes. Individual flowers are about in diameter, each with five horn-like hoods and five pollinia. The seeds, each with long, white flossy hairs, occur in large follicles. Fruit production from self-fertilization is rare. In three study plots, outcrossed flowers had an average of about 11% fruit set. Ecology More than 450 insect species feed on A. syriaca, including flies, beetles, ants, bees, wasps, and butterflies; it is an important food source for monarch butterfly caterpillars (Danaus plexippus); other species that feed on the plant include red milkweed beetle (Tetraopes tetraophthalmus), the milkweed tussock caterpillar (Euchaetes egle) and Oncopeltus fasciatus and Lygaeus kalmii. Many kinds of insects visit A. syriaca flowers, and some kinds pollinate them, including Apis mellifera, the Western honey bee, and native Bombus spp. (bumblebees). In the U.S. mid-Atlantic region, the introduced species A. mellifera was found to be the most "effective" pollinator, but this occurs more often among flowers of the same plant; since A. syriaca has a high level of self-incompatibility, it is less effective than 'Bombus spp. in the fertilization of flowers because Bombus spp. are more likely to visit unrelated individuals. Monarch butterfly larvae consume only milkweeds, and monarch populations may decline when milkweeds are eliminated with herbicides. The development and widely adopted cultivation of herbicide-resistant staple crops such as corn and soybeans have led to a massive reduction in weeds and native plants such as milkweeds. Subsequently, this has played a significant part in the population decline of the monarch butterfly. In 2018 the CEO of the National