Ability to ID to a group of visually similar species within a genus

See discussion in https://www.inaturalist.org/observations/29763522 for examples.
While identification to species may not be possible, the default to ID to genus level is too broad in some cases. The Genus Desmia has two species that cannot be distinguished without a ventral view, but these species are identifiable from the rest of the Desmia species. Having a selection for “Desmia funeralis/maculalis” would allow the most specific ID possible in many cases. The Genus Xestiahas a similar issue where tow species can only be differentiated based on a 6 mm difference in size limiting ability to make distinction using a photo that doesn’t include a scale. Having the option to chose
“Xestia c-nigrum/dolosa complex” would allow the most specific ID possible in many cases.

Heck yes. As an identifier I’ve wished for this many times. A few more examples:

Birds: Lesser vs. Greater Scaup. They’re in the diving ducks genus Aythya, which is large, but all the other species are easy to identify. Someone renamed the genus “Scaups and Allies” last year, possibly because of this issue, which annoys me.

Spiders: Theridion frondeum/albidum. Theridion has several sibling species pairs. https://bugguide.net/node/view/486191

Fungi: Chlorociboria aeruginascens/aeruginosa. I’ve been told these two can’t be distinguished without using a microscope to examine the spores, or with DNA analysis.

My only worry is that these might not be established taxonomic categories. On the other hand some subgenera would be so useful for identification that it might be worth adding them as deviations anyway.

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I’m pretty sure this was discussed on the Google group some time back, with the iNat position being that “slashes” that aren’t recognized taxa are discouraged. I would be interested in that discussion being revived.

This also runs into the thorny issue that not all difficult to identify groups or pairs of species are monophyletic. This happens a lot in birds (the group I am most familiar with). For example, Lesser and Greater Yellowlegs (both currently in genus Tringa) are frequently confused by U.S. birders but are not sister species or closely related within their genus. It seems like it would be confusing to include paraphyletic taxa in a classification scheme like that used in iNat.

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Species complexes/groups are already allowed and can be incorporated into the iNaturalist taxonomic framework. This covers some of these cases that have been mentioned. From the Curator Guide:
https://www.inaturalist.org/pages/curator+guide#complexes

Species Complexes

As of January 2019, “complex”, a taxonomic rank between genus and species, may be used (more specifically, between subsection and species). Species sometimes intergrade and there are places on the tree of life where adding hard range map boundaries is arbitrary and/or identification to species level is often not possible. Species complex should be used sparingly (only when necessary and helpful) and with the following criteria:

  • Species complex is monophyletic (i.e. sibling groups of species)
  • Complex is recognized in the literature
  • A named subgenus, section, or series does not already exist for the group
  • Use the earliest published species name for the name of the complex
  • Don’t use compound names, such as Pantherophis alleghaniensis-spiloides, as there may be numerous species in the group
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Here’s the original discussion, if you’re interested: https://groups.google.com/forum/#!searchin/inaturalist/rufous$20allen$27s|sort:date/inaturalist/sPqtgqVv3kU/FUSQ5vwMAwAJ

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I’m not sure I fully understand the concern with using slashes in this Tringa example. You’re concerned that the slash (i.e., Lesser/Greater Yellowlegs, like eBird allows) will leave folks with the erroneous assumption that these two species are super closely related I think. They are in the same genus, though–how closely do they have to be related? Perhaps a more extreme (although slightly silly) example that we’d both push back against would be something like “Volucella/Bombus”, where Volucella is a genus of flower flies that closely mimic bumblebees. I think we’d both agree that we wouldn’t want to see iNat allow that designation. However, I definitely see the difference between your yellowlegs example and the examples by @pachips and @JeremyHussell. Another example of a potentially good use of slashes would be for cryptic species complexes that are composed of an unknown number of species. Lots of examples from insects, including the scalaris group of Calligrapha beetles: https://bugguide.net/node/view/502240/bgpage).

The guidelines shared above suggest that all taxa in iNat should be monophyletic. I guess that could be changed, but for now it seems like that is an important part of how taxa are defined in the database.

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For the record, I actually think these type of “slash” taxa (like those in eBird) are a good idea, I was just pointing out the monophyly issue.

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To avoid “slash” and “sp.”, maybe we could add multiple taxa to an ID? Like a hummingbird that could be Allen’s or rufous, it would let us enter both names and it would create a genus name ID with those two species noted.

Suggested ID: Selasphorus
possibly: Allen’s hummingbird, rufous hummingbird.

I agree that adding complexes, especially to a lot of aviary and insect species would be a great idea. And here’s a couple examples on why I believe it’s needed.

Empid species: Pacific-slope/Cordilleran Flycatcher, Alder/Willow Flycatcher, Dusky/Hammond’s Flycatcher – A lot, if not all empids can be identified to around two species, such as the ones I mentioned above. However, by photographs, it’s difficult to id them from photos because you need a call. I thought complexes would help a lot.

Pacific Treefrog: 13 years ago, herpatologists did the stupidest thing possible with the Pacific Treefrog and split them into 3 species because of mtDNA differences but didn’t bother figuring out ranges/visual differences between them. Yet there are dozens of species of Pseudacris genus species. A complex for an ill-split species is needed desperately.

Sharp-shinned/Cooper’s Hawk: Probably the two hardest Accipiters to identify from each other. I think a complex between the two could help those that are inconfident with their id or for those where id can’t be determined from photos.

I do agree though that if we make complexes, they should be in the same genus. So I would find Lesser/Greater Yellowlegs complex acceptable but not something like Red-tailed Hawk (dark morph)/Harris’s Hawk. So I think careful consideration of each complex is needed.

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Could this issue not be resolved with a a species complex, as done so here for Narceus americanus and N. annularis?

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Yes, but see @bouteloua’s post above about the criteria for adding those complexes. The first two criteria exclude many of the examples discussed here.

It looks like that Narceuus example also violates the naming convention in those criteria ;)

This particular complex contains only two species and was pulled directly from how it is displayed in literature, so I don’t think this is a significant issue.