Hoya yuennanensis was first collected in 1915, but was not published until 1936. In 1977 botanists Tsiang & Li believed that H. yuennanensis was a synonym of H. lyi, but Michele Rodda in 2012 said that they are clearly two separate species:

“It is clear from the examination of the lectotypes and of the cited specimens of

Hoya lyi and H. yuennanensis that there are two separate species, both ecologically

and morphologically. Hoya lyi is a small lithophytic species with variable leaves that

can be oval, elliptic or oblong. It is found only on limestone, in deep shade, growing

tightly appressed to the rock surface. Hoya yuennanensis, in contrast, is a more

rampant climber, generally with elliptic or oblanceolate leaves found on siliceous and

limestone outcrops in exposed locations. Both species have white to pale pink

flowers of similar size but they can be easily discriminated by the shape of their

coronas. Hoya lyi has a rather flat-topped corona with rounded and flattened

slightly ascending outer corona lobes while H. yuennanensis has erect corona lobes

with rounded outer processes and a depressed stigmatic head (Fig. 1). They can also

be discriminated in their pollinia: Hoya lyi has smaller pollen masses with an

elongated retinaculum while H. yuennanensis has a massive retinaculum compared to

the size of the pollinium (Fig. 2). For these reasons Hoya yuennanensis should be

reinstated.”

https://www.researchgate.net/publication/259418725_Taxonomy_of_Hoya_lyi_Hoya_yuennanensis_and_Hoya_mekongensis_Apocynaceae_-_Asclepiadoideae

Here are the specifications of the conditions that made Hoya yuennanensis flower for me. Potting substrate was coconut husk mixed with 20% large sponge rock (Perlite). Went outside in June to increasing day length hours, and flowered as the day length shortened in late August. Temperature ranged from day time highs of up to 85 F to night time lows down to around 50 F. Watered with nutrient solution once per week.

Finally on my 35th wedding anniversary, the buds opened! Maybe it was saving all of its blooming splendor for a gift, but whatever made it flower, I will never know for sure. As beautiful as the flowers are, the fragrance is even nicer! The smell perfumes an entire greenhouse and is among the most powerful that I have experienced since I have been keeping Hoyas.

I have neglected to point out thus far that there has been many times over the years that my miserable little starts of Hoya yuennanensis put out peduncles, but they never produced any buds. In the spring of this year (2023) I started the plant over for at least the tenth time since I got it way back in 2016. I started a few pots of it, and took one cutting of it and started it with Hoya aff. thomsonii. In the summer, I decided to put it outside in the greenhouse for the heck of it as I could not remember if I had grown it that way before or not. In late July, I almost fell on the ground when I went to water it, and saw that an old peduncle had actually started to bud up! The buds got bigger week after week until they looked like this!

Months of bad growing, slowly turned into years of struggle with this plant. I had tried it in every Hoya growing mix known to man, but always the same pattern of re-root and deterioration would repeat. I came close to throwing it out on numerous occasions, but was loathe to, because it was one of only a couple of plants that I had in my collection from the legendary Toril Nyhuus. Below the leaves of Hoya yuennanensis:

I wish that I could say that this little cutting did well for me out of the gate, but it grew only sporadically and not particularly well at any time. The usual pattern was that I would grow it for around 6 months and be forced to start it over. The plant was exceptionally easy to root; it would put on a few leaves and then just languish and usually need to be started over again because of root rot.

I received Hoya yuennanensis as a tiny four leaf rooted cutting in the spring of 2016. It came from an order that I made from Torill Nyhuus using Julie Kennedy as an intermediary. This was the same order that included the all white flowered Hoya Bella (PES-03).

Tomorrow I begin my discussion of Hoya yuennanensis. This has been a perennially difficult Hoya for me to grow, and up until this week a plant that has never flowered for me. The wait is over!!

I wish that I had more information on this plant, other than acquiring it from Indonesia. If anyone knows any additional info, please let me know. I believe that Hoya aff. lambii (SLM 04) is a plant best left to completist collectors as it would never make it in the regular house. I believe that it needs very warm, humid conditions in order to thrive. That being said, the flowers are quite nice to experience in person, and the plant is somewhat easier to grow that the original Hoya lambii.

Here is a photo of the entire plant. You can see that the plant does not have to be very large in order to flower. I have now flowered this plant on numerous occasions on two different peduncles. It appears to be one of those plants that is easy to bloom, but hard to grow well.