Tropicals & Tender Perennials: H. carnosa Snowball - NOT! But it's interesting...., 1 by markroy68

markroy68 wrote:
As a wise woman I know is fond of saying- "Hoya carnosa- WHO CARES!!!"
Seriously, though, the subject of H. carnosa and H. motoskei has been covered very thoroughly several times by Christine Burton, most recently in her P. S. The Hoyan V.4 #4:

http://www.psthehoyan.com/psthehoyan4_4.htm

A very helpful photo comparison of the flowers was placed on this forum by Christin Karllson a while ago. I'll move it here, I hope you don't mind Christina!
While these two plants confusion in horticulture and taxonomy is an interesting topic, it is also confusing and very involved. The thing to keep in mind is that these two species involve different collections from different locales and have consistently different leaf and flower size/shape, the easiest way to distinguish them being the leaves, as seen above.
An argument could be made that these are two different ecotypes of the same species, but that would be the subject of long debate and needs more study- not an easily answered question for amateurs (like me) to argue out.
It does make you wonder how Hoya taxonomy is ever going to progress in the public eye, when so much confusion is continuously generated over the two oldest (to cultivation) and most common hoyas in existence.