Milk′weed, species of Asclepias, a genus of the milkweed family, which contains about 85 species, mostly natives of the western hemisphere, nearly 50 occurring in North America.  The name comes from the fact that they contain a milky juice which exudes from wounds.  They also are often called silkweeds from the large pods containing numerous seeds bearing beautiful tufts of silky hair.  These seeds with their downy sails are of much interest.  One of the most attractive forms is the butterfly-weed or pleurisy-root (A. tuberosa), whose flowers are bright orange and in midsummer clothe the dry pastures of New England in masses of brilliant color. The stem is from one to two feet high, but contains little “milk.”  The other forms are taller and have chiefly purplish to red flowers, occasionally white.  The flowers are much modified for insect-pollination, the pollen-grains clinging together in masses which are carried off by the insects bodily.  Probably the commonest known milkweed is A. cornuti, also known as A. syriaca.  The weed has a stout, tall stem and opposite leaves, six to eight inches long.  In early summer it puts forth flowers of purplish pink, blooming from June to August.  The two pods are full to bursting of seeds with lovely, silky tufts.