Gurmar or Madhunashini meaning "destroyer of sweet" is a rather ordinary looking creeper with an extraordinary property.
According to Flowers of India website "is a famed plant, revered for its use in treatment of diabetes for nearly two millennia."
Try this simple experiment:
Chew a leaf of this plant and then eat some sugar.
The grains of sugar will be as tasteless as sand!
This effect remains for quite sometime afterwards (i've never actually checked the duration, but guessing a couple of hours at least!)
True to it's name, madhunashini "destroys" the sensation of sweet. But more than that, it has a beneficial effect on the management of blood sugar too, and hence it's widespread use in Ayurveda and alternative medicine for the treatment of diabetes and some other ailments.
More on this from the Karnataka horticulture department here and Wikipedia here.