Karl Foord - Extension Educator, Horticulture
Swamp Milkweed (Asclepias incarnata) as you know is an important plant for Monarch Butterflies. The plant also produces significant amounts of nectar and thus attracts a host of other pollinators including various bees and ants (Photo 1).
On close examination the flower structure is bizarre. Typical corollas face backward (Photo 1), whereas prominent coronas fold to form a tube of sorts out of which a horn projects toward the center of the flower. The stamens have fused to form a cylinder around the pistil with a pink stigmatic surface in the center (Photo 2).
Pollen has fused to form wings called pollinia which are connected by a dark pollinarium gland, the whole structure being called a pollinarium. You can see the wings protruding from the side of the fused staminal column (Photo 2). The strategy is for an insect to visit the plant looking for nectar and catch its leg on one of the pollinia wings which detaches from the plant and attaches to the insects leg. The insect carries the pollinarium to another flower where the horn may help in detachment placing pollen on the stigmatic surface.
I took many pictures hoping to find an insect with a pollinarium attached to its leg. Alas I did not find one. However, I did find pollinarium that had been transferred from another flower. They can be seen in Photo 3 where the top center section has three pollinarium and the top left section has two pollinarium where originally each had only one.