How are species complexes treated?


How should organisms be identified if what inaturalist considers a species is in the literature considered a complex of several, including undescribed, species?

It has come up in an observation of enchenopa binotata. The opinions appear to be that since it is a species complex, it should receive genus level ID. That seems wrong to me. If E. binotata refers to the complex, then any member of this group should get the E. binotata ID. Perhaps the taxonomy should call it a complex rather than a species. But I’ll be the first to admit that I don’t know what I’m doing.

Looking at other such cases that I have noticed, Pantherophis alleghaniensis appears to be explicitly a complex in the inaturalist taxonomy. Narceus seems to require using the genus level ID for the n. annularis/americanus complex.



You will probably find that complexes are usually where there are two or more taxa and specimens will sit somewhere between them. It just means you need to pick which species description it is most like. You have to remember that a species description is based on a single specimen, and often characters are not black and white but cover spectrums, like black Vs grey, and when does grey become black…



If I’m reading it correctly the iNat taxonomy now seems to include the taxon rank of ‘complex’ which I hadn’t noticed before. So in your example there are two entries for Pantherophis alleghaniensis. One is Pantherophis alleghaniensis Complex, which includes, as child taxa, all the species in the complex, and that includes Pantherophis alleghaniensis again, but now being used in the strict sense.

It’s an interesting idea, although I imagine it will confuse some people. There is no formally recognised taxonomic rank of ‘species complex’ in any of the codes as far as I’m aware. Sure, you will see ‘species complex’ used in the literature as a term to qualify a taxon name (and not so different to using ‘aff.’ or ‘cf.’) but it has no formal standing in nomenclature. I know only formal scientific names are allowed in the iNat dictionary (no tag names) which I can understand. But why is this bit of nomenclatural rule-bending so different?

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I don’t think we should be identifying observations to species if there’s no safe way to separate them. In cases where there is cryptic species or species that are impossible to separate without dissection (e.g. Many insects, Arion slugs, possibly Northwestern/America Crow on the west coast, etc.) either genus level or a holding bin field or a new “taxon” would be better.

My understanding is that since this January species complexes are officially allowed (an issue with Narceus is that there used to be a species complex “taxon” and they were ID’d to that, but then it was removed so they were all identified arbitrarily to one of the two species, or to genus, causing a mess).
I’m not sure if there’s a specific definition for a “species complex” to avoid an infinite amount being made? What’s the difference between a subgenus and a species complex and a tricky pair of species?

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Holding bin fields are fine as a temporary placeholder but i don’t think we should be using them in the long term. They don’t work with any of the other filters or lists or the range maps. I’d rather just have the complexes when we can. In the past we weren’t able to do so, so i’m glad that was changed. A lot of times in large genuses, identifying to genus when you know it’s one of two or three species is a waste.



A subgenus contains species that are thought to be descended from a common ancestor. A tricky pair of species can be difficult to distinguish, but aren’t necessarily closely related. A species complex involves hybrids or incompletely separated species. I think all species complexes would technically be part of a subgenus, but a subgenus could include a species complex plus closely related species whose ranges don’t overlap or don’t hybridize for some other reason.



Seeing that complexes are part of the inaturalist taxonomy, and that this is a relatively recent addition, perhaps the best course of action would be to flag the taxon in question for curation. I’m going to try with enchenopa binotata.

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So I was just pointed at:, which is sort of the answer for the question I meant to have asked. (thanks @bouteloua)

That leaves cases outside the guidelines, but sometimes it may be appropriate to use genus or species even if it’s ambiguous.

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