On Natural Variation in Hoyas
I was reading this article on natural variation the other day and got to thinking about just how messed up Hoyas are when you consider the frequency that new plants are considered to be new species instead of just natural variations of known ones.
Most recently there was a photo of a very narrow lance shaped leaf of a plant that was collected along with Hoya thompsonii. Now to me this was obviously just a variation of Hoya thompsonii and showed all the characteristics seen in this species but it was listed as an unknown. Granted the plant was not shown to be in flower so the conservative thing to do would be to keep it as an unknown until it can be confirmed but having said that variations in leaf do not make new species. Sadly the Apodagis site seems to be offline, hopefully it is back soon as it is a great resource.
Now the article above is tailored to Aroids and there will be terms used that do not apply to Hoyas. Hoyas also do not show Ontogeny which greatly simplifies identification. Plants like many Aroids and Nepenthes have distinct life stages where the fully mature flowering portion of the plants can look very different from younger plants and in the case of Nepenthes the pitchers used to catch insects can also change quite dramatically on the high climbing or upper portion of the plant vs the initial lower growth.
I would recommend everyone to read this article as it will help in understanding that plants of the same species do not need to look exactly the same. We see this with Hoya carnosa plants that people post, there are many leaf shapes associated with Hoya carnosa but often times people feel that they have something different because it is not the carnosa they are familiar with.
A very good point is made in the article about the collection of plants in the wild. Plant collectors choose the best or most novel specimens to introduce to horticulture, not necessarily the most common form of a species. When Hoyas are concerned, because they are so easily propagated vegetatively one new introduction can spread throughout collections to the exclusion of others. Even though you may get one plant from Thailand and another from Sweden in some cases they may very well be from the same original source.
I hope the article helps in understanding some of the issues faced by Hoya collectors and why the names can seem so confusing. As RFG has pointed out we obviously have many species under the wrong names and others that perhaps should not have been published as new species have been. This all makes me wonder just how many of our "species" are truly hybrids that have developed to be stable over many thousands of years. Still as long as we try our best to follow the rules of nomenclature we have a terrific structure in place to help us discuss these plants.