I know little about this species other than I bought it as an unrooted cutting in the summer of 2018 from Ric Morier on eBay. I suspect that it was something he brought back from one of his trips to Vietnam. It was a fairly pricey cutting at $28 so I suspect that it is somewhat rare. In addition, as of this writing there are no other photos of this plant to be found anywhere.
The cutting rooted quickly and moved from a series of net pots until in flowered in a four inch pot. It is a plant that uses very little water. The leaves are lovely getting a reddish brown color in good light. The flowers have little to no scent, are about 3/8 of an inch in size, and last about 4 days.
Hoya hainanensis is a lovely plant with nicely scalloped leaves and gorgeous flowers that is not very hard to grow. It flowers in a reasonable amount of time, and is a plant that I can recommend to everyone. Let’s hope that it becomes more readily available in the future.
**Update January 31, 2019** I just heard from Ric morier about the history of this wonderful plant and here it is in his own words:
Someone gave me a heads up that you wanted to know more about this species. I just saw your YouTube video and congratulations on blooming it.
So here is the story on that Hoya. I met Ngo Minh in Saigon and we arranged to go west and meet Hong Nguyen. We had a hard time communicating as my Vietnamese is nonexistent and their English was slightly better than my Vietnamese. So needless to say… I found myself on a mopped for over two hours headed towards West Vietnam
not far from Cambodia. I was exhausted as it was like 98 degrees.
Hong and her family were so lovely and friendly and I could of spent days with them.
She had lots of rare Hoyas, a lot of them looked to have been recently collected in the surrounding area.
The VN Vietnam attracted my eye for the lovely reddish foliage so I asked Hong for a piece. She took a sharpie and wrote the name on the leaf. I assumed it was collected in Vietnam, probably in the surrounding mountains. I will try and reach Hong and see if it has been given another name.
As you said on the video, it is very rare in collections.
If you could possibly send my a picture of the bloom, it might help Hong to ID.
I’ll send you some pics from that day back in Dec-2015.