Intrigued by knowing more on this Asclepiadaceae I tried to find information exceeds it and I did not find anything. I looked for species of pink flowers in Europe and the Mediterranean basin and I did not have luck either. Between the photographies on Vincetoxicum that shows the Google finder is no similar one.
Three years ago an eminent French scientist, René Sforza, contacted with me by email. He is very interested in seeing plants of Vincetoxicum nigrum of Majorca, because he was making a study of the plagues that affect this plant in order to find a natural enemy that it serves for the biological control against the Vincetoxicum nigrum introduced and feral in Canada and north of USA, where this Mediterranean plant has proliferated as much that it has become an uncontrollable plague. Don't mention it they have served chemical products, because it turns out to be resistant to them.
I spoke him of the Vincetoxicum of pink flowers and we went to see it in the botanical Garden. It said to me that it knew tens Mediterranean and American species of Vincetoxicum, but those pink flowers were not known for him. He suggested that perhaps it was a hybrid, but that stops to assure its identity made lack a genetic study.