I’m no botanist, but scientists say that he big difference between the two plant are that the coronal scales of H. merrillii are sloped upward towards the outer tips such that the outer lobes are raised higher that the center of the flower. I have no idea what they are talking about, but here are flower photos of both plants as sold to me. Hoya merrillii came from Ted Green in Hawaii and Hoya quinquenervia came from Aleagarden in Thailand