Hoya rosarioae is very similar to Hoya obscura but has smaller flowers, much longer peduncles and the pollinina are much shorter. This information comes from a Dale Kloppenburg publication, but I can attest that this plant is a different animal than H. obscura.  I have tried to grow Hoya obscura on two seperate occasions and failed – it won’t grow for me under my conditions, but Hoya rosarioae grew very easily. Below the back of the flowers: