Suggested change to curator guide: hybrid taxa of different ranks

The curator guide says:

“Hybrids should only be made between taxa of the same rank. Hybrids like Canis lupus × canis lupus ssp. familiaris don’t make sense. That’s like saying you made a new kind of vehicle by combining the traits of a Honda Civic and a car.”

I recommend changing this to:

“Hybrid taxa should not be created in iNaturalist if one parental taxon includes the other. Hybrids like Canis lupus × Canis lupus familiaris don’t make sense. That’s like saying you made a new kind of vehicle by combining the traits of a Honda Civic and a car.”

As it currently stands, the first sentence indicates a policy, the second and third provide a rationale that does not support that policy. The problem with Canis lupus × Canis lupus familiaris, as explained by the reference to Hondas & cars in the following sentence, is that one parental taxon includes the other. This is a subset of the broader category of hybrid formulae with parental taxa at different ranks. It does not provide any grounds for rejecting the broader category, and at the moment I can’t think of any reason to do so.

The topic came up in this discussion. I figured a new topic was warranted, since in that one it was not apparent to me that there was a specific issue with how part of the curator guide was worded.


Addendum: an additional sentence like this might also be helpful:

“If creating a hybrid taxon with parents of different ranks, give the name of each parental taxon in full, for instance Setophaga coronata auduboni × Setophaga townsendi rather than Setophaga coronata auduboni × townsendi.”


At present there are three kinds of hybrid taxa available to choose from when creating a new iNaturalist taxon: GenusHybrid, Hybrid, and InfraHybrid. I think some questions may need to be addressed before settling on a general rule for hybrid taxa in iNaturalist.

GenusHybrid: intended for hybrids between different genera, parented directly to the next higher node containing both genera. (Lots of examples in Poaceae tribe Triticeae.) A named hybrid would by definition be between two taxa of the same rank (genus). For example Genushybrid ×Elyhordeum.

Questions: when creating a GenusHybrid taxon using a hybrid formula instead, would we want to allow such formulas to specify subdivisions of different genera (like subgenera or sections) for one or both parents? Seems like that could get pretty messy, especially as infrageneric nodes are revised over time. If we do allow such formulae, should they be restricted to the lowest-level infrageneric rank(s) recognized within each genus? Or are we ok with GenusA × GenusB section C, even when GenusA contains subgenus and/or section nodes?

Hybrid formulae between different subdivisions of the same genus may be a different matter, but only in that the iNaturalist rank GenusHybrid may not have been intended for them. As hybrid formulae, however, they are easy enough to accommodate if desirable. Personally, though, I would prefer to keep things simple here and restrict GenusHybrid taxa to hybrids between taxa of rank Genus.

Hybrid: similar issues and questions as above. Intended for hybrids between different species, parented directly to the next higher node containing both species. A named hybrid would by definition be between two taxa of the same rank (species).

When using a formula instead, I think infraspecific taxa could be included as long as they belonged to different species. But again, should they be restricted to the lowest-level infraspecific rank(s) recognized within each species? Or are we ok with speciesA × speciesB subspecies C, even when speciesA contains subspecies or other infraspecific nodes?

InfraHybrid: not as certain about the intent of this rank, but if analogous to the others, it would be for hybrids between different subspecies (varieties, etc.) of the same species, parented directly to that species. Hybrid formulae between subspecies belonging to different species would fall under the rules for the iNaturalist rank Hybrid instead.

Because of the nomenclatural equivalency of the different infraspecific ranks in plants, I think we have no choice but to allow InfraHybrid formulae between taxa of different ranks, as long as they are both infraspecific ranks within the same species.

I’ll note that the ICNafp Article H5.2 states

If the postulated or known parent taxa are at unequal ranks, the appropriate rank of the nothotaxon is the lowest of these ranks.

If we are only dealing with hybrid formulae, I don’t think this impacts any of the above, but if hybrid names (nothotaxa) are involved it could become an issue.

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And another note: the format for hybrid formulae currently recommended in the Curator Guide (“the pattern GENUS SPECIES1 × SPECIES2”) is directly contrary to ICNafp Article H2.1 (Example 2).


Stop, you’re saying a hybrid of two subspecies of the same species is available? But we’re told it’s not.


If that’s not what the InfraHybrid rank is for, then I hope someone else will chime in and let us know what its intent is.

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I haven’t really interacted with these different hybrid categories in iNaturalist and I’m not sure what functional role they have.

From a nomenclatural viewpoint, named hybrid taxa are a different category of thing from hybrids designated by hybrid formulae. The former have names governed by the rules of the ICNafp, the latter do not.* Hybrid formulae are discussed in the ICNafp and their components are ICNafp names. Hybrid formulae themselves are not names. They do not have ranks, do not follow any of the rules related to publication, authorship, or legitimacy of names, have no effect on the nomenclatural status of names, and so on. The ICZN—I think, I hope someone who knows this code better than I will correct me if I am wrong!—gets to an equivalent result by a different path. Named hybrid taxa have names governed by the ICZN and there is no discussion of hybrid formulae beyond “that’s outside our scope”.

While the effects of past decisions play a role here, a data structure that both lumps fundamentally different nomenclatural categories together and makes terminological distinctions that aren’t found in either code is not very appealling. Unless there’s some real benefit to assigning rank categories to hybrid formulae, why not just follow the codes? Don’t worry about it. Hybrid formulae do not have ranks. And then maybe go all the way, put the names of hybrid species in the same category as the names of species and so on (with a separate “hybrid” marker, as desired), mark the hybrid formulae in some convenient fashion as “not names according to either code” and link their component names to, well, their component names.

*Named hybrid taxa have a confusing rule set. The short version is: We can add an “×” to the name of a taxon, and add the prefix “notho-” to any rank-denoting terms, as a way of marking the name as applying to a hybrid taxon. The “×” is not part of the name; Alpha ×beta is the same name as Alpha beta. Similarly, “nothosubspecies” and “subspecies” are nomenclaturally identical ranks. Both the “×” and “notho-” can be added or subtracted without requiring any nomenclatural act. However, the ICNafp also includes rules that specifically apply to names of nothotaxa, like Article H5.2. Here’s how I think this is supposed to work: Suppose there is a hybrid between Alpha beta and Alpha gamma var. delta, and I’m going to publish a name for it. If I choose to mark it as a nothotaxon, all the “H.” rules of ICNafp apply and my name needs to be at varietal rank. If I don’t mark it as a nothotaxon, none of the “H.” rules apply and I can publish the name at whatever rank I want. Suppose I take the second path and I publish it as Alpha epsilon. Next year Author writes a revision of Alpha and treats Alpha epsilon as a nothotaxon. If Author identifies the parents of Alpha epsilon as Alpha beta and Alpha gamma, Alpha ×epsilon is kosher. If Author identifies the parents as Alpha beta and Alpha gamma var. delta, Author needs to create a name at new rank. I don’t know what species it ought to be put under, as neither Alpha beta nor Alpha gamma make biological sense and creating a new nothospecies name just to have a place to stick Alpha […] var. ×epsilon is kind of silly.

Frankly, this is a dumb rule set. And it is entirely optional. Marking something as a nothotaxon is a deliberate choice to inflict the mess of the “H.” articles on ourselves. I do not understand why anyone makes this choice. If we want to say that Alpha epsilon is a hybrid, write: “Alpha epsilon is a hybrid.”

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All true enough. The practical reality on iNaturalist, though, is that every taxon record created has to be given one of the ranks made available by iNaturalist. Otherwise iNaturalist doesn’t know how to construct its taxonomic tree, adjudicate ID disagreements, etc. Taxa based on hybrid formulae have to be accommodated in that system too, somehow. And I think they can be fairly easily. To me it’s just a question of how much formula craziness we want to encourage here based on how meager evidence. The current rule and guidance keeps it fairly restrictive, which is likely a good thing, but as you’ve pointed out, better wording and some exceptions may be necessary.

In that context, the correct treatment of something like Setophaga coronata auduboni × Setophaga townsendi seems pretty obvious: The parent is Setophaga, ID disagreements should kick it up to Setophaga.

Accomplishing that by having the data say “this is a taxon at species rank” is not ideal—it isn’t a taxon and it isn’t at species rank. Having an additional field can be an inelegant but effective solution. For instance, one might have true / false field called something like “isCodeCompliantName” and then be explicit in associated documentation that: “rank” in the iNaturalist data structure ≠ ICZN or ICNafp rank; to convert iNaturalist “rank” to Code rank, make yourself a new field that is populated with iNaturalist “rank” values when “isCodeCompliantName” = “TRUE” and left null when “isCodeCompliantName” = “FALSE”.

Having a data structure that just sticks hybrid formulae in there without warning downstream data users that there a bunch of deliberately false values in the data or telling them what to do about it, on the other hand, would be a severe enough error that the only reasonable response would be to correct it. Often, our past mistakes just need to be fixed, convenient or not.


The data won’t say that. They will say that the taxon is at Hybrid rank (in this case), or GenusHybrid or InfraHybrid rank, and the rank of it’s parent will be a further indication of what level of hybrid it is. Though equally inelegant, I think that conveys the same information as the data structure you are suggesting.

In iNaturalist, anything that supports an ID is a “taxon,” whether or not it is code-compliant. My preference is to keep the number of non-compliant taxa to an absolute minimum, and I think that is the spirit behind the current Curator guidance on hybrids as well.

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You’re right, I was writing quickly rather than carefully. :-)

I’m not sure I get to a more optimistic assessment by being more careful, though. The issue is the distinction between Alpha ×epsilon and Alpha beta × Alpha gamma. As I understand it, both are given the iNaturalist-rank “hybrid”—at least, this is implied by the curator guide switching between examples of the two categories without distinguishing them, and I just checked a few examples of nothospecies, all “hybrid”. However, Alpha ×epsilon is a species-rank name* under the ICNafp, Alpha beta × Alpha gamma is not a name and has no rank.

As a result, “hybrid” partially overlaps with the set of species-rank names and “species” is a subset of the species-rank names. To interpret this accurately, downstream data users would need to know that not all species-rank names in iNaturalist are in the “species” category, that “hybrid” includes both species-rank names and hybrid formulae, and have some way of distinguishing the two dissimilar categories** within “hybrid”. This is arguably not as bad as dumping all the hybrid formulae with two species as parents into “species”, but it’s more complicated and probably more difficult to correctly diagnose and interpret.

I’m not at all opposed to using designations other than Code-compliant names, by the way. In some contexts, I’ve been one of the more vocal advocates for including such designations. They just need to be marked in a way that’s unambiguous and easy to use. Having fewer of them doesn’t help that much—if they’re there, the data format needs to make the difference obvious.

*Keeping in mind that nothospecies are species—Alpha epsilon and Alpha ×epsilon are the same name.
**It’s tempting to think that there would be a relatively easy way to do this with some rules for parsing the character strings. For instance, if the “×” is the first character after the first space, it’s a name of a hybrid taxon, not a hybrid formula. Having tried to do this with several different nomenclatural data sets, though: Sure, it’ll work—if the data are very well-formatted and consistent—and the data aren’t.


That’s a strange example given that iNat’s taxonomy treats domestic dog and wolf as separate species.


In my opinion, it should be okay to designate a hybrid between two terminal taxa even if one taxon is a monotypic species and the other is a subspecies of a different species. To me it’s more informative. The example I used on another thread was the hybrid slider turtle Trachemys gaigeae x T. scripta elegans. (The first species in this combination, T. gaigeae, was formerly split into two subspecies but is now considered monotypic. And all known hybrids are the result of interbreeding with one subspecies of T. scripta.)


The reason why I’m so insistent on this change is because why aren’t species-like taxa are not deserving of a hybrid taxa. The example I used in my thread was the Gibraltar Buzzard, a hybrid “swarm” between Western Common Buzzard (Buteo buteo buteo) and the Atlas Long-legged Buzzard (Buteo rufinus critensis). These hybrids are common and “pure” individuals of either species is difficult to find in the Gibraltar regions. Outside of this small region in Spain and Mocorro, Common and Long-legged are quite rare and usually only occur when a Northern Long-legged (ssp rufinus) ventures too far north of its normal breeding range, thus hybridizing with Western and Steppe Buzzards (ssp. buteo and vulpinus).

Additionally, several taxonomists have advocated to the speciation of the Atlas Buzzard (Rodriguez 2013) but it was usually shut down due to the uncertainty of identification. But preliminary genetic evidence (Jowers 2019) has shown the Atlas Buzzard is in fact more closely related to the Common Buzzard than the Long-legged Buzzard. That means the Atlas Buzzard is either, (A) a full species or (B) a subspecies (Jowers specifically coined the term “allospecies”) of the Common Buzzard. That means the Gibraltar Buzzard is a very different “hybrid” than other Common x Long-legged hybrids.

Assuming in the future that we refer to option B for the Atlas Buzzard, that would make the Gibraltar Buzzard an intergrade population, even though we’ll coin it on iNat as Buteo buteo buteo x critensis, that doesn’t mean it’s not a valid taxon. Junco hymealis cismontanus or Cassiar Junco is now believed to be an intergrade swarm between Oregon and Slate-colored Juncos but we are now calling them Junco hyemalis hyemalis x oreganus, it’s J. h. cismontanus, a subspecies. Heck, what about hybrid speciation? The Audubon’s Warbler is in fact a hybrid “species” between Black-fronted Warbler (Setophaga nigrifrons) and the Myrtle Warbler (S. coronata), but we don’t call it Setophaga nigrifrons x coronata, it is Setophaga auduboni. Couple other examples include the Italian Sparrow (Passer italiae) which is a hybrid between House (Passer domesticus) and Spanish Sparrow (P. hispaniolensis). Or Hawaiian Duck (Anas wyvilliana) being a hybrid between the Mallard (A. platyrhynchos) and Laysan Duck (Anas laysanensis). Point being, just because it’s a hybrid doesn’t mean it shouldn’t be or avoided on iNat. Look at plants.

@birdwhisperer I don’t disagree with anything you’ve said here. The examples you gave were of parent taxa at the same rank, thus fitting the current Curator guidance. This topic is about whether that guidance needs to be tweaked to allow hybrid formula names with parents at different ranks, like

speciesA x speciesB subsp. C.

Personally I agree that, within limits, allowing finer ranks on one or both parent taxa would be more informative, when well-documented and not just speculative.

That said, I’ll just point out to everyone the lead paragraph of the section on hybrid taxa in the Curator Guide:

Given their vague morphological delineation and taxonomic uncertainty, use of hybrid taxon concepts should be avoided whenever possible. Adding IDs of higher-level taxa is usually sufficient. In those rare cases when some external authority actually supports a named hybrid, we will tolerate it…

Unless iNaturalist changes that fundamental position, creation of hybrid taxa on iNat needs to remain judicious, whether or not the same-rank guidance is adjusted.

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