"discovering" new distinguishing marks on iNat

Has anyone else noticed new (at least to them) distinguishing characteristics while identifying species on iNaturalist?

Sometimes when I’m reviewing observations of closely-related species on iNaturalist I realize that there seem to be other characteristics that distinguish them that aren’t mentioned in the key I’m using. In other words, I’ll sort them according to the key, and then notice after-the-fact that “wow, species A always has X characteristic whereas species B never does, and instead always has Y characteristic.” Sometimes X and Y are more obvious (especially from photos) than the distinguishing characteristics in the key.

I’m not claiming that I’m discovering the difference for the first time. Just realizing it myself. X and Y may well be described in formal species-descriptions of A and B, they just don’t seem to make it into any keys I’m aware of. Or maybe they do and I’m just forgetful.

Uvularia grandiflora and Uvularia perfoliata are frequently-photographed wildflowers in my region. They look similar. Keys tend to emphasize differences in leaf-underside hairiness, internal flower structure and texture, branching patterns, and subtle differences in tepal color to distinguish them. These characteristics are not always evident in photos. But after applying those differences (when they are evident) I noticed that the tepals always twist along the long axis in U. grandiflora and inroll at the margins in U. perfoliata. This trait is readily apparent in nearly any photo of a blooming plant. After noticing this, I tried to find a scholarly source describing this difference, but I couldn’t readily find one. I did find some comments to this effect on some iNaturalist observations. I can see why this difference wouldn’t make it into a key. This characteristic relies on fresh tepals, and might disappear in flattened herbarium specimens.

Is it fair for me to appeal to these “emergent” differences to distinguish species?

I could see this going awry. For example, maybe they’ve been omitted from a key because some (presumably quite rare) populations don’t fit this pattern. But on the other hand, isn’t iNaturalist all about learning from nature? I’m curious to hear the community’s thoughts.


Keys use signs seen on herbarium specimens and often only those that are most consistent and enough for id, you’re right that there’re more differences than you can find in keys!

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I think this is a great use of iNat (finding these characters) and that they are legit to use. People who are experts in organisms in specific locations can often distinguish specimens from one locality or another with pretty good confidence based on characters that aren’t in field guides.

I think the only thing to keep in mind is that the characters you notice may not 100% distinguish species if there hasn’t been a systematic study (rare populations are one example, traits that are variable even within a population or species another). But even characters that are 95% accurate are still very useful! So I think it’s totally legit to use these but also keep an open mind to notice cases where the characters might not be consistent or something like that and take other characters into account too.

If you can find someone studying them or writing the next field guide, maybe it can be validated for the future!


For insects, flies especially, most of the keys online tend to be made for specimens. I’ve created several keys of my own for photo ID for genera, and many of the features I use are new, or at least not recorded in a guide.


@gcwarbler has worked on this for Cisthene moths in Texas and the southern US: https://www.inaturalist.org/posts/17268-an-interview-with-gcwarbler


I have absolutely seen this. And both ways, too… I have struck cases in literature where the description very clearly states a given pattern (this is in spiders), and I have struck occurences confirmed by genitalic examination that show the pattern character is not always present. A field worker often develops gestalt clues for identification that might be around behavior or posture that is not evident in literature that give descriptions of specimens from collections. And sometimes you see a (spider for me) case that looks exactly like every other one you have seen, except for a behaviour that is remarkably odd, such as making a web in a different structure, or being found around human habitations when they are not normally so… and then closer inspection reveals them to be a different species!


Thanks, Tony, for mentioning that research. For a new paper on the moth genus Petrophila coming out later this year, I studied thousands of images on iNaturalist precisely to elucidate useful pattern characters that help descriminate among a set of species where the formal published taxonomic works rely primarily on genitalic characters or a few simplistic field marks. It’s fun detective work!


I remember a mammalogy internship I did. When we had a chipmunk in-hand, obviously, we sexed it using the most obvious method. But I noticed that the males all had slightly pointier faces than the females.


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