Per the International Code of Nomenclature (ICN) for algae, fungi, and plants (Art. 50 and Art. H.10.1 Note 1), changes like this are considered trivial nomenclaturally. Such changes (in either direction) do not involve a change in rank or authorship, nor do they require formal publication. Anyone can express an opinion that a published species name is or is not a hybrid simply by writing the name with or without the multiplication sign.
For that reason, I would suggest that there is no need to make taxon changes in iNaturalist for simple changes in hybrid status like this. It amounts to a “spelling change” for something that is already “spelled” correctly according to the ICN. Instead we can just add the hybrid or non-hybrid variants of the name to the scientific name synonyms to ensure the taxon can be found in iNat under either variant.
The name and taxon are not changed by adding or removing a “×”. So, presumably a “taxon change” is not needed when the taxon hasn’t changed.
When a change is needed for some other reason, and there is an option to include the “×” or not, personally I would always omit it. I view this “×” business as a mistake in ICNafp that I hope is corrected at some point, a holdover from an era when people thought a hybrid species wasn’t a “real” species and needed a special marker. By now, of course, we know that hybrid speciation is common in plants. If we used the “×” for every species with a hybrid speciation event somewhere in its ancestry, we’d probably have to include it in every last binomial.
In modern usage, the “×” seems to be more like a question mark, a way of saying, “I don’t think this is a species but I’m giving it a binomial and treating it as a species anyways.” Why we need a special provision in the nomenclatural code to help people engage in this kind of self-contradictory waffling is a mystery. :-)
Hybrids are not species (and “speciation” by hybridization will require that entire populations of hybrids occur and replace the parents - undoubtably there are examples. And there are examples of Frankenflora where human translocation creates hybrid swarms which invade and replace the local parent.). Yes, there are many cases of species that evolved by hybridization: but those are valid species in that they are populations interbreeding individuals and usually the parent species no longer exist.
But many hybrids have been formally taxonimically described by mistake: on the assumption that they were valid species. Taxanomically they are valid names: types, descriptions, etc. But in reality they are a few individuals within (sympatric, relatively genetically isolated) populations of the parents. These names should be regarded as mistakes - errors of typification of taxa at species or infraspecific rank, and I prefer to see them synonymized under the hybrid formula. That applies also to selected cultivars of hybrids that are now common worldwide such the London Plane (Platanus occidentalis × orientalis or Platanus × acerifolia (or the synonym Platanus × hispanica))
So my vote is for all hybrids to be treated by their hybrid formula.
I agree with you that nothospecies designation is often misused for independently reproducing species of hybrid origin. I think it can be appropriately used, though, for recurring spontaneous hybrids that are sterile, or at least that rarely backcross with their parents. The hybrid swarm situation that @tonyrebelo mentions is more of a gray area where personally I am most inclined to use the hybrid formula approach instead.
This is all a matter of taxonomic philosophy and opinion, though, not anything dictated by the ICN, which allows any of the above naming methods. My question is more around how iNat taxonomy should or should not respond to differences in such opinions, especially in the (likely) majority of cases where we will not be in a position to evaluate the status or parentage of a putative hybrid or species of hybrid origin.
My suggestion is that if the iNat name otherwise conforms to ICN requirements, there is no need to change between equivalent hybrid/non-hybrid formats for a taxon name, at least without clear knowledge of and consensus around the origin of a putative hybrid.
@jdmore: I agree entirely with you on this: “My suggestion is that if the iNat name otherwise conforms to ICN requirements, there is no need to change between equivalent hybrid/non-hybrid formats for a taxon name,” although I would leave out your “at least” clause. :-)
@tonyrebelo: By “hybrid species” I think I mean the same thing you do by “species that evolved by hybridization”. Our semantics differ, but that aside I think we are in agreement. Using a binomial with an “×” to name something that is not a species is a mistake. If it’s not a species, use a hybrid formula. If it is a species, use a binomial and omit the “×”.
It’s of course worth mentioning that this is more-or-less an issue that has only occurred in botanical taxonomy. Examples of hybrid species in other groups such as mammals and birds were never indicated by this symbol.
For those who are unaware, a “hybrid species” is not equivalent to a “hybrid”, according to the usage of that term. Instead it is considered more closely equivalent to a genuine species, but with known recent parent species that converged and established as a unique, consistent genetic entity. It’s incredibly subjective in terms of how taxonomists decide whether a species in this context should be a “hybrid species”, marked with the symbol, or a “regular species”. There’s no measurement here as far as I know besides arbitrarily. However, it is still a useful state to mention when the parentage is known and confirmed.
Because of the ambiguity of the term “hybrid species,” I always try to be more precise by calling it a “species of hybrid origin” – if that’s what it is. Which, by the way, many things we now take to be “regular species” likely were at their origin, at least in the plant world!
In practice perhaps, but not necessarily so, since the tools are readily available to determine whether a population is an independently reproducing species that happens to be of past hybrid origin (to which the × symbol need not be applied), versus a collection of continually generated hybrids between extant parents (to which a × name or a hybrid formula more appropriately applies).
I’d still call this subjective as some authors see a timeline where this symbol no longer becomes necessary. For instance, a species with a well-documented hybrid origin that has shown to keep distinct for a long period of time (years, decades?). In those cases I’ve seen authors opt to drop the × symbol because even though it’s a known origin, the plant has isolated itself “enough” that it’s no longer used.
I agree, choice of rank will always be subjective when we are temporally close to the origin of a new taxon. Things in transition tend to defy objective categorization.