Taxonomy - name changes

I apologise for the naivety of this query, but …

I’m noticing that some plant names used in Australia (which appear in the Australian Plant Census) are not accepted by iNaturalist (which I understand uses the taxonomy of Kew’s Plants of the World Online). Examples I’ve encountered so far are:

Blechnum cartilagineum (APC) - Oceaniopteris cartilaginea (PWO)

Hybanthus monopetalus (APC) - Pigea monopetala (PWO)

I understand why name changes become necessary (discovery of earlier names, new information about evolutionary relationships, etc), but what I don’t understand is why the name changes don’t settle down more quickly and become universally accepted.

Doesn’t the International Botanical Congress Nomenclature Section make final determinations on these matters? Are there disputes about the validity of the changes? Is it because national herbaria lack the resources to do the work necessary for updating?


Hi @helen_y, not a naive question at all, and certainly one shared by many. I’ll do my best to shed a little light…

For the examples you gave (and in most examples of name changes these days), it comes down to the choice of a taxonomist whether to lump a group of species into one large genus, or to split them into smaller genera. There are many scientific factors that go into such decisions, but in the end they are arbitrary and subject to differing opinions.

The Code of Nomenclature maintained by Botanical Congresses provides the various ranks (like genus and species) available for taxonomists to use, and the rules for determining the one correct name for a taxon with a particular type, rank, and circumscription. It also provides for “conservation” of younger or otherwise incorrect names over older correct names, when doing so would avoid undue nomenclatural instability.

Beyond that, however, the Code does not tell a taxonomist how to arrange species into Genera, Families, or any other rank categories. That is up to their interpretation of the available scientific (hopefully) data on those species, which these days generally means their evolutionary history as inferred from DNA studies.

Once evolutionary lineages have been settled, however, it is still arbitrary as to whether to put several lineages of related species into a single large genus, or divide them into smaller genera. A taxonomist who wants their classification to have the best chance of gaining universal acceptance will want to put a large dose of common sense into their decision.

Choice of genera is particularly important, since the genus name is part of the species name, and so the most “visible” part of the classification. Are my genera easily recognized and distinguished by ordinary practical characteristics? Do they make evolutionary sense? Etc.

Sometimes there are pretty clear answers to those questions, and other times it’s a coin toss. And that’s where names can continue changing back and forth between different genera (like your examples), depending on the whims of the day. In general, a classification that strikes the most practical middle ground between the extremes of lumping and splitting will have the best chances of long-term acceptance. But it can take a lot of back-and-forth to find that middle ground, and then new scientific discoveries can sometimes throw a big wrench into the works and start the process over again.

Wish I could tell you that someday names will become completely stable, but that would be the day that scientific discovery ceases, and/or nomenclature becomes a dictatorship. Definitely hoping neither of those come to pass.

As for choice of POWO over APC, iNaturalist had to decide on a single worldwide taxonomic framework for each major group of organisms, to maintain as much stability and consistency as possible within iNaturalist. But it does allow for “deviations” from that framework when there is some reasonable consensus in the iNat community. So if you find yourself really disagreeing with the POWO classification for a particular taxon, you can always flag it for curation, and explain in comments why you think a different classification should be followed on iNaturalist. Many such deviations have been implemented over the years, when there was agreement to do so.

Hope this helps, and I’m sure others will have different perspectives to add also.


thank you for the thorough explanation!

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In addition to plants, where two or more synonyms in current use seems to be quite common, there is also a lot of taxonomic flux these days in many other groups of organisms. Herpetology is going through a period of much disagreement about genus and species names. Molecular systematics has upended many assumptions about relationships and in some cases there is an “over-exuberance” in splitting and reassigning species based on rather preliminary genetic data. The pendulum swings one way, then back again, and we probably need to just accept that a truly stable taxonomy in certain groups might be untenable.

Every scientific name is a hypothesis about evolutionary relationships and is subject to acceptance, rejection, or revision. (Once I accepted that, the name changes didn’t really trouble me anymore.)


@helen_y : thans for you question. Complementary to the answer of @jdmore, I wuld like to add one important aspect.
Names that you cited in example are nomenclatural names, i.e. exact and reciprocal unambiguous synonyms. Then we could change one to the other without difficulty, and then change back the second for the first without difficulty again. So it is easy to do it (a simple “swap”).
But for the same reasons, these two names are representing exactly the same thing are users don’t really need one more than another and can use which one proposed by iNat even if which one they usually use is the another. This is possible and easy because they can put they name, and the synonymy automatically consider it under the other name.

Contrarily, the debate is open for cases of taxonomic synonymy, which means non-reciprocal and ambiguous synonymy, i.e. several taxa described separately are considered today as synonym, but some people can disagree and prefer to distinguish under a non-used name. This case is more problematic, because they cannot used the differentiated name (automatically replaced by the programme) and if finally they’re right, we cannot a posteriori separate the former-synonym without reconsidering one-by-one each observation…
Am I right ?

You are right, this is often the case when formerly lumped taxa get split apart again. If the split taxa have completely or mostly separate geographic ranges, however, iNaturalist has a helpful tool called Atlases. An Atlas can store the geographic range of any taxon, and when available, is used by iNaturalist to assign observation IDs to the geographically correct taxon when a split is implemented. The downside is that if the observation is in a place where atlases overlap for two of the split taxa, it will get assigned to the common ancestor of the two taxa, and will have to be identified manually.


I’m not a big fan of subspecies since too many are rather poorly defined and will likely be discarded or elevated to full species whenever someone gets around to it. But in cases where there is disagreement about whether we are dealing with one species or multiple species, the inclusion of the subspecies name when IDing a record can be helpful.

For example, iNat still recognizes one species of marten (Martes americana) in North America. Most mammalogists recognize two, M. americana and M. caurina, with a narrow zone of overlap in the Central Rockies where separating them might be tricky. At some point, iNat might split the records for these two forms into two species to conform with current taxonomy. But in the mean time, it’s probably helpful to ID the Martes in much of western North America as M. americana caurina, in anticipation of that revision and to make it easier to accomplish in the future.


Thank you all for the detailed and considered responses to my query. I am new to iNaturalist and continue to be amazed at the generosity of moderators and community members with their time and expertise. I am learning so much.

I am still left with curiosity as to the process of acceptance and adoption (or rejection) when a taxonomist proposes a reclassication/name change. As there seems to be no central international authority that says ‘OK. You’ve convinced us. That’s what we’ll all go with from now on”, what happens? Is the decision to adopt the change up to individual countries (their national herbarium) or perhaps individual institutions within each country (state herbaria)? What might cause delay of adoption?

As an example, another disparity I’ve discovered in the last few days since my original post is with the little herb that we in Australia know as Hybanthus stellarioides. In POWO/iNat it is Afrohybanthus stellarioides. I’ve found the scientific paper proposing this new genus:

Flicker, Benjamin and Ballard, Harvey E. (2015). Afrohybanthus (Violaceae), a new genus for a distinctive and widely distributed Old World hybanthoid lineage Phytotaxa 230(1):39

My confusion is - five years after this paper was published, the Australian Plant Census still uses Hybanthus stellarioides and includes no reference to the new genus Afrohybanthus. Why the delay? Is because:

· we are slack down here?
· Northern hemisphere botanical institutions are better resourced than ours and can update their systems more quickly?
· we disagree with the American splitters?

I probably should ask the question here in Australia.


There is no authority that says a newly proposed scientific name shall be accepted. What typically happens is the new name is published – whether it’s a new species, the elevation of a subspecies to species, change in genus, or a resurrected name that has not been in use for a while – and it is evaluated by the specialist community at large. It might come into use rather quickly, especially if some other authors and their publications use it, or it might be ignored. Sometimes it will be used by some but another name will be used by others. The top experts in the field might be able to sway the community one way or another as to what name should be used. It’s kind of a free for all, but (hopefully) a consensus will arise over time to adopt or reject the name. Kind of messy but that’s how it works.

I think it was Carl Sagan who said: “There are no authorities in science, only experts.” And the experts often don’t agree.


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