Hydrangea-mystery plant III, Ecuador

In the past five years, there have been a number of small vines coming out of South America, mostly from Ecuador.  This is the third of this type that I keep and is distinguished by the three-point serration on each leaf.  The two other types are very similar, bright green and very small leaves, one from Peru and a second Ecuadorian species.  Overall it seems to be a rather slow-growing group of plants, but once acclimated they can put out moderate growth each year.  They seem to require a vertical surface to climb.   Otherwise, they will not put out much new growth and can stagnate for years at a time.  This one was on sphagnum for years and hardly grew, but is now finally taking off on a tree branch.  I think they would do best if treated similar to orchids.

As for the true genus of this plant, it remains a mystery! Hydrangea has not been discounted as far as I know, so for referencing I am putting that for now.  If anyone has a better guess, please comment below or contact me!