Black swallow-wort is a relative of milkweeds. These flowers are only a quarter inch, so they're not much like those fascinating milkweeds, but the pods are just like milkweeds. The fuzzy seeds waft along in the breeze, and have been successful at spreading black swallow-wort far and wide. It invaded from southwest Europe, and is far too common in our open spaces. It can clamber over and wind around our natives and kill them off. It is said to have once eliminated a whole field of goldenrod. Black swallow-wort is also a roadside plant, and my hypothesis of the day is that it is most common where the roads parallel the prevailing winds. That is my experience with it, but my sample size is fortunately not significant. This species is a significant pest in CA, CT, IL, IN, KS, KY, MA, MD, ME, MI, MN, MO, NE, NH, NJ, NY, OH, PA, RI, VT, WI, ON, and QC. Lenawee Co MI, 5/21/12. Dogbane family, Apocynaceae.