Hmm. I guess I didn’t think about it that way. I think it could be easily interpreted either way, but your interpretation is probably closer to what was intended. Regardless, it really needs to be edited for clarity.
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@tiwane Regarding the curator guidelines concerning species complexes, the writing is not very clear. Do you know by what process it is usually edited?
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I mostly like this.
I don’t see any difference between 3 or more vs. species pairs. In fact, it might be even more important when it is just a pair. That said, the more species pairs there are, the more complexes there could be. So, I guess that may be where you are going with that. We don’t want a complex for every pair of species that are hard to tell apart and that should maybe be stated in the curators guide.
But there should be a literature review and ideally consultation with experts first. Many groups don’t have adequate literature or any current experts, so it makes perfect sense for an iNat person to take on that role and name a species complex if it is useful for the iNat community and if it may lead to future clarification between those species.
I would also maybe add that “a significant enough amount of observations that would benefit from the change” should include a significant amount that are problematic to ID to species. If there are 500 observations within the complex and only 10 are confusing, it’s probably not necessary there either.
Personal thoughts:
- Any ‘grouping of species’ deemed a useful addition on iNat should be somehow supported by external (non-iNat) usage or reference - i.e. showing that there really is some real-world difficulty with the taxa, not just a transient lack of skills or of identifiers on iNat
- Since such a ‘grouping of species’ could not be achieved the ‘official’ way (e.g. by replicating some Subsection from the Reference Framework), it should be made explicit that (a) it is an in-house creation (b) which has some out-of-house basis, cf. 1.
- The addition of such ‘grouping of species’ should not depend on a minimal number of observations (except if 0 obviously: no obs yet? no need yet); just like other taxonomic additions to iNat, it is amply justified as soon as the first observation requiring it is uploaded - immediately enabling appropriate ID for all later obs.
Now unleash hell
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I would as @loarie, he’s in charge of the taxonomic stuff. I mean, techincally any curator can edit the Curator Guide but for policy stuff any changes should be okayed by a staff member.
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Replying specifically to you saying:
I think this is true. However, the only people suggesting complexes are well-versed enough in that taxon or taxa to know the complex is necessary, so there’s no risk of unnecessary complexes made in my opinion (and experience).
We either accept that we have the power to make complexes without a needed citation, or accept that most of the needed complexes cannot exist because there is no citation. I very much side with the former.
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Or we say people should cite when possible and provide justification when it is not. This justification can then be cited.
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Justification example: “Insertion of a species complex is necessary and sensible in this case (Myself, right now)” 
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I am generally in favour of adding complexes in a flexible and utilitarian manner, but not on a personal whim. Yes someone obviously has a certain amount of knowledge if they are suggesting a complex, but they probably don’t have universal knowledge of the taxa - so consultation is important.
As far as monophyly goes, I’ve always taken the explanation in the curator guide to mean that it is just insisting that they must have the same taxonomic parent. (i.e. don’t try to make a complex between a species in Xylota and species in Chalcosyrphus just because they look similar.
As examples of the above: I helped organise Platycheirus taxonomy a while back, and one of the things I wanted to achieve was to replicate the species groups used by the UK recording scheme. But I had to check with workers in other countries that it wouldn’t tread on their toes, figure out if there were non-UK species that also needed to be included in certain of the groups, and ensure that they were compatible with the wider literature-based taxonomy we were trying to implement (oh, and pleeease do vote for this if you agree btw! https://forum.inaturalist.org/t/create-a-new-taxon-rank-for-inaturalist-the-species-group/14543 )
I was able to implement most of the groups - and I could find literature references to tell me what extra non-UK species should be included in them. But there was one I could not implement with the UK definition because its members were spread between different subgenera (it is a group of convenience for recording, but not natural), and one other that I had to include a species that the UK scheme puts in a different group. Basically, I had to accept a more internationally applicable definition. This is the sort of process I think the curator guide is calling for.
I agree with those who don’t think it is necessary for a paper to exist explicitly and exactly saying ‘There is such-and-such a complex’, but there should be an indication in the literature that these particular species constititute a recognised group of similar species. This I think is simply to avoid the taxonomic anarchy of people making up whatever they want, and including whatever they want in it. We are trying to be followers, not inventors of taxonomy. Having said that, there are some instances where a little exercise of judgement ought to be excused when the literature answers most, but not quite all of the relevant questions.
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Going back to the question of the monophyly criterion, I don’t know that I like this criterion for a couple reasons:
- Clades required to be complete.
- Paraphyletic groups are not acceptable.
- Monophyletic groups often don’t correspond well to practical problems of identification.
It turns out to be not as bad as I remembered with the E. hyssopifolia complex, but such a complex could not include E. vermiculata without including E. anychioides, probably all of the Pacific Island endemics, and quite a few very different taxa from Asia. The phylogeny comes from Yang and Berry’s phylogeny of Euphorbia sect. Anisophyllum. I wouldn’t mind including E. anichyoides to make the thing paraphyletic instead of polyphyletic, but under no circumstances would I want to include the Asian taxa that look nothing like E. hyssopifolia. Alternatively, I could exclude E. vermiculata as I find if fairly easy to distinguish, but it is one of those traditionally considered difficult to separate from E. nutans. I’m leaning toward the last option, but I will be defining the taxonomy. As an expert in this group, I have no problem doing that and I think it makes the most sense pragmatically. But the main point I want to convey is that there is an inherent conflict between the monophyly criterion and practical considerations of identification.
As such, this becomes a question of the primary purpose of “species complex” as a taxon. Is it to act as a simple taxonomic rank between species and section? Or is it a pragmatic tool used to represent uncertainty? In the literature, you get both, though favors the latter. The best practice is probably to stop calling it a complex once you know the relationships and use terms more like clade or group (since I’m getting my Ph.D. working on resolving a species complex, this is good for me to think about). The terminology is too loose for anyone to actually follow that, though. Regardless, I think allowances should be made for both. But if that is the case, we shouldn’t really have a monophyly criterion.
Furthering this case, there are actually taxa in plant taxonomy that were chosen knowing that the groups were paraphyletic. They aren’t particularly common, but if we do want to follow taxonomy and not invent it, the monophyly criterion really has no place here. That said, I think species complex represents a taxon where we can’t help but doing a little inventing of taxonomy given the limitations of the literature, the problems of identification, and how disconnected the literature can be from the problems of identification.
Hmm, that seems doubtful given how specific a term monophyly is. But if that is the case, the curator guide is even more misleading than I thought. Taxonomy is not phylogeny.
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In principal, I agree. In practice, I’m not sure. The problem there is that half or more of the taxa within sect. Anisophyllum would probably end up in a species complex, especially with a strict monophyly criterion. There are very few species where there aren’t some taxonomic uncertainties either at some part of their range or in the context of one very similar species. Few difficult species on either sides of a clade can end up roping in a lot of species into a complex. I’ve only picked out the E. hyssopifolia complex because it is by far the most difficult to deal with. I have used observation fields for most complexes with lower numbers of individuals.
I think that traditionally a species complex is a group of morphologically similar taxa where the relationships between them are hypothesized to be closely related to each other but whether they are or not is unknown. This means that they may or may not be monophyletic. In many cases they have been shown not to be. Some people may call a clade of morphologically similar taxa a species complex as well but, once those relationships are established as a clade, it is perhaps better to call it a clade.
Because iNat has a tree-based taxonomic structure, I think for iNat the “monophyly” of species complexes would not necessarily be true monophyly but monophyly within the iNat taxonomic structure. For example, if the Euphorbia sections conflicted with the species complexes, you should only have one or the other. And, if one is more useful than the other, it is perhaps the better choice to use the more useful one even if not truly monophyletic. And, of course, wanting everything to be monophyletic relies on an oversimplification of relationships that just doesn’t fit the reality of the more complicated relationships between some taxa, especially those sorts of taxa that end up getting called species complexes.
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To anyone writing about iNaturalist’s taxonomy in the future, please, please, please, do not use the word monophyly in this way. Monophyly is a specific term that refers to groups correspond to clades in an evolutionary context. It does not refer to the nested hierarchical relationships in a taxonomic framework.
If someone want’s to convey that a taxon cannot be a subset of more than one taxon, they should state that. That or simplify it to something better.
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Well, if some spurge afficionados somewhere in the world - as evidenced by external sources - have felt and expressed the need for that many species “complexes” (or “aggregates” or whatever - not sure if strictly equivalent in concept) in order to deal with hundreds of difficult taxa… why shun that on iNaturalist? because POWO The Reference does not implement them?
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Because it can cause a lot of confusion:
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Yep, it happens. IIRC there’s even a bug report or feature request somewhere, to have a ‘Complex’ not appear higher / not get selected in place of the ‘real’ species, in lists of suggested names (e.g. when automagically grabbing a name from EXIF metadata, or when entering it manually at the Obs Upload screen). Could be extended to the Search function maybe, to exclude ‘complexes’ from results. Or make them appear lower. Or sort/display them differently. Or…
Now, how terribad are the consequence(s) of that “confusion”? IMHO, very minor (it takes literally seconds to fix, when mistakenly IDing as ‘Complex A b’ instead of ‘A b’). Or so serious that the use of ‘complexes’ should be reverted, if too detrimental to the functioning or usability of the search engine. (Which would also have the welcome side-effect to bring iNat closer to POWO, in its shunning of too many ranks)
edit: speaking of broken search engine, how deeply-flawed and confusing is that? 
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;)
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Your Euphorbia question is meritorius, more than rehetorical. I have the same challenge for my small group of beetles (just 170 spp). In some literature, even subgenus is just ignored, while in just about all literature, species groups are ignored. I studied these buggers for many years and even now, some folks put them on ignore, to the detriment of the knowledge gained and communicated. So my solution is to elevate the groups that merit it as genera and force the issue. It’ll p**ss folks off in some places (well they have to reorganize their museums and such, eh), but let them refute my elevation in status in public, in publications, and prove me wrong. Historically, taxonomy changes, does it not! Linneaus and Fabricius weren’t right all the time, and knowledge changes and evolves and improves. Old World folks don’t always think the same as the New World folks, either, so it can get kinda political. Taxonomic changes are the result of those changes. My vote is: compile your data and evidence, and publish the Euphorbia changes - sandmats versus candelabra trees versus poinsettias, all in the same genus, really? 2000 or more species in the same genus just doesn’t make alot of sense when infrageneric categories don’t get accepted. Maybe Coleopterists think differently from botanists but there are more beetle than plant species and the same challenges exist
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I also believe that species groups can be very helpful, especially in large genera with many species and many observations. I would not require the most strict application of the principle of monophyly because our knowledge is constantly changing and because I believe the primary purpose for species groups is to bring some sort of structure to genera that are a “black hole”. Species complexes should be recognizable without most advanced expert knowledge. They serve to make genera with hundreds or thousands of observations and dozens of species more tractable. If all we can apply is a genus ID the observation falls into the “black hole” and it becomes really difficult to find for experts who may in fact be able to get it to a species. So I am all for it. But yes, please don’t create species complexes just for the sake of adding more taxonomic units to the framework. A genus with five species and twenty observations does not really need species groups. We can handle it just fine the way it is.
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What could be acceptable threshold(s) to reach before iNat implements those ‘species complexes’ already in wide use in the outside world?