A. tuberosa

Asclepias tuberosa

Butterfly milkweed


Dogbane Family

Butterflyweed is the only orange-flowered milkweed in the mountain region.  It is a species of open, sunny spots.  This species lacks the milky sap of most milkweeds, but it still contains the cardiac glycosides that make milkweeds poisonous.  There is a long folk tradition of using milkweed in small doses in a variety of medicinal applications, inspiring Linnaeus to name the genus for Asclepius, the Greek god of healing.  These chemicals are feeding deterrents to most herbivores, but a number of insects have independently evolved means of detoxifying them and so are able to specialize on milkweeds, even turning the plant’s defense into their own by sequestering the glycosides.  Insects and other animals that are capable of this trick often advertise their unpalatability with bright, contrasting colors — aposematic coloration.  Interestingly, several of these milkweed specialists have converged on the same warning color palette of orange, black, and white.  The most famous of these is the Monarch Butterfly (Danaus plexippus), but in our area you can also easily find Milkweed Tiger Moth caterpillars (Euchaetes egle), Milkweed Bugs (Oncopeltus fasciatus), and Milkweed Beetles (Tetraopes tetraophthalmus).

Another interesting feature of milkweed biology is its mode of pollination.  Like orchids, they deliver their pollen in tiny packets called pollinia, gluing these to the legs or proboscis of insects.  Look closely at the intricate flower structure: the corolla consists of 5 reflexed petals, at the base of each of which is an odd stamen modified into a tube-like structure, termed a hood, each with an inward-projecting horn.  Collectively the hoods make a crown-like structure called the corona.  If you look carefully you can see a tiny dark oval-shaped glandular structure between the hoods.  This gland forms the top of a slit-like opening between the anthers, within which the paired pollinia are hidden.  Unsuspecting insects probing at the nectar-producing gland insert a leg or proboscis into the slit, where the pollinia become attached. 

A. tuberosa Map

Weakley, A.S. 2020. Flora of the southeastern United States. University of North Carolina Herbarium, North Carolina Botanical Garden.