Already have a cool humid growing environment for, say, pleurothallids*? Sarmienta scandens might just be the gesneriad for you. Check out Jacob Uluwehi Knecht's photograph of a Sarmienta scandens flower, complete with ruler and many informative links. Did I mention the links? Yes, click on all of them, and see S. scandens growing on a tree, and how the flower and leaf compare to Mitraria coccinea.
*Those be orchids.