Asclepias, commonly called butterfly weed, is a Missouri native perennial.  It boasts a long bloom period from June through August and can tolerate dry conditions.  Butterfly weed is late to emerge in spring but is very reliable and long lived.  This plant is great for naturalizing a garden area.  The flowers attract butterflies and hummingbirds.  The flowers are a nectar source for the monarch butterfly larvae (caterpillars).