There is no documentation that provides guidance to curators about when to subdivide a genus. I recently flagged a genus to be subdivided but consensus was lacking so I posted a general forum article on infrageneric subdivision. That feedback was helpful but at least one curator felt it was inadequate so I’m posting a followup here hoping to find consensus among curators on this topic.
Assuming plants are typical (that’s all I know), it’s not unusual for a genus to have incomplete phylogenetic data. In some cases, there may be no phylogenetic data at all. This brings up one question in particular: Is it advisable to subdivide a genus based on morphology alone?
To get the ball rolling, here’s a short list of requirements that have surfaced:
The infrageneric names of the proposed subdivision MUST be valid.
The proposed subdivision MUST be supported by one or more citations from the scientific literature.
The proposed subdivision MAY be supported by morphological data but phylogenetic data SHOULD be brought to bear on the proposal whenever possible.
The proposed subdivision MUST be comprehensive and global.
The proposed subdivision SHOULD be stable.
I’m using MUST, SHOULD, and MAY in the sense of RFC 2119 for clarity (or maybe that’s confusing, I don’t know).
Questions to be asked during the subdivision process:
I’m not sure about zoological names but botanical names must be validly published names. Are the proposed names registered in IPNI?
Have all taxa been taken into consideration? (This is not to say that all taxa must be placed.)
Does the proposed subdivision lead to better data in the iNat database?
If you have comments, questions, or suggestions, please post them. TIA
I’m supportive of ranks between genus and species when it makes a very speciose genus easier to work with. For example, if it narrows down the number of possible species in a genus that contains 100 to maybe 10 within a subgenus. Especially in cases when you can’t get an observation down to species but it can be placed in a subgenus or section. The White Pines in my area come to mind.
For all intents and purposes, a genus should only be subdivided when this subdivision is recognized in literature and/or is recognized in a database used as a reference for the group.
Exactly this. iNaturalist is descriptive of recognized taxon frameworks, not prescriptive. Adding any taxa that are not either formally recognized in the scientific literature or within some sort of recognized taxonomic database is not how this site is to be used.
I’ll do a short answer since i had developped my point of view in our related flag. :
Genus subdivisions should be as describe for complexes in our curator guide :
Monophyletic : or at least the key nodes, we do not have always a complete valid phylogenic tree to fill it entirely, but that’s another brick in the wall aslong as it is consistent with the current existing taxonomy. Only morphology-based taxonomy is inconsistent with the remaining taxonomic base of iNaturalist and is very likely to be entirely wrong in a “natural” phylogenetic tree approach, that have been ruling taxonomy for 30 years now. For many genus recent work is lackin, but nothing hurry in adding subgenus division. Their miss doesn’t prevent the correct use of iNaturalist.
Based on litterature : iNat is not a place to create an autonomous taxonomy based on “expert-talk”. Source(s) must be as much accesible as possible for anyone, we don’t have to be an expert to understand choices. Beside I think it’s ok to fill some taxa in a node, that has not be cited in said source(s), because the taxa conception has change (i.e original species 1 is split in species 1 and species 2. Ok to add tacitly species 2 in the same infra as species 1).
Validely published taxa : personnal opinion, i think it should be at least registered in an authority taxonomy base. Idk for other taxa groups but for plants i would suggest to only add names that have been recorded in IPNI. That’s also something i really would like to see for POWO’s deviations.
Anyway an update of the curator guidelines looks required for me, those discuss has become more more frequent in iNat, du to the increase of infrageneric nodes implement.
If we are going to use the complex guidelines for other infrageneric ranks, it might be worth mentioning another guideline which as far as I know has only ever been mentioned by staff on the Rufous/Allen’s Hummingbird flag:
I’m not aware of this guideline generally being followed strictly and I don’t think most curators are aware of it. I’m not super familiar with these hummingbirds given I live out of their range, but from what I know of them they seem like a situation where a complex be helpful…
In general, avoid subdividing taxa unless it actually helps with identification. And any new subgeneric taxa need to be recognized in the literature. iNaturalist curators should be making curatorial decisions, not taxonomic decisions. We should be looking at what taxonomy is most current and prevalent in the literature, not what taxonomy most matches the morphological or phylogenetic data. Most iNat curators only understand enough about phylogenetics to be dangerous, not to make accurate taxonomic decisions. For example, I’ve seen cases where iNat curators have argued for taxonomic changes in birds based solely on mitochondrial DNA data. If you know much about birds and mitochondrial introgression, you will understand why that is a mistake, but many well-educated people have a simplistic understanding of genetics and think all phylogenetic trees are equally trustworthy. Apparently (from what I’ve been told) it is common in iNat plant curation to create species complexes based on original, unpublished research, which I think is a mistake and should be discouraged. There’s a reason we have peer-reviewed journals and arcane nomenclature codes. It isn’t just to slow people down with bureaucracy. It’s because not everyone actually knows what they’re doing.
Based on comments, I probably need to illustrate with an example.
Consider a genus of flowering plants distributed across Europe, Asia, and North America. In the 19th century, an Old World botanist named and described two sections, placing each of the Eurasian species in the appropriate section. Later a New World botanist placed the North American species in the same two sections. Most if not all keys in major floras published in the last 150 years include a couplet that distinguishes the two sections (if not by name, at least by description).
As of 2025, some phylogenetic results have been published but not enough is known to further subdivide the genus. Is there sufficient evidence to subdivide the genus into two sections?
Primary literature is fine, but the clades need to be defined and named, not just present in a key or phylogenetic tree. Otherwise we are doing original taxonomic research and creating new taxa, which isn’t our role.
This is opinion based, but i think when a genus is so unwieldy large it is nearly inhuman to learn all the species it should be subdivided.
Ultimately taxonomy is a human construct and it should try to be as useful as it can be. Unsubdivided genera with 1000s of species are so large it’s hard for the human brain to grasp.
This isn’t a route for iNaturalist to take, more so taxonomists, but if a genus has like 3000 species, maybe it would be more useful bumping the diagnostic definition of the genus to something higher like subtribe, and dividing it into genera.
I’ve encountered similar choices about whether to subdivide plant genera. To be clear, I’m talking about subgenera, sections, etc. that have validly published names. As @upupa-epopsmakes clear, POWO is not going to come to our rescue here as they don’t concern themselves with ranks between genus and species. Here’s what I have done:
After quite a while working with Sisyrinchium, I decided that it was worth my effort to implement the 10 subgeneric sections outlined in Inacio et al (2017). Some factors in favor here were based on utility for iNat users: It’s a fairly large genus (~200 species), with some easy to identify and others very hard to distinguish, meaning that a lot of observations can be placed confidently in a section but not refined to species. The quality and likely durability of Inacio’s paper was also a big factor. She performed a phylogenetic of 110 taxa across all sections, and she then tied that back to consistent morphological traits for each section, with a clear identification key. After adding the sections to iNat, I populated them based on the Inacio paper, and on other primary sources that provide unambiguous guidance. Despite that, there are still 48 species not placed in any section at this point.
Echeandia has similar identification challenges, with 80+ species in the iNat taxonomy. Robert Cruden was the main 20th-century researcher working with this genus, and in 1999 he divided it into two subgenera. Nevertheless, I’m content to leave the iNat genus undivided for now. Cruden’s subgenera seem like a work in progress; unsurprisingly, he wasn’t able to ground them through DNA sequencing, so they’re based on combinations of morphological and phenological characters. These may be valid, but they’re far from clear cut. Subgenus Mscavea generally includes low-altitude species with white flowers that open late morning or afternoon and have narrow inner tepals. But some species in subgenus Echeandia also have white flowers and others also grow at low elevations. And some species in subgenus Mscavea grow at moderately high elevations or have yellow or orange flowers. So the distinctions are messy and unhelpful, and it seems better to wait for future research.
Polianthes, with 24 species, illustrates another reason not to split a genus. Here about half the species have moth-pollinated, erect, white or pale pink flowers and fall into subgenus Polianthes, and the other half have hummingbird-pollinated, pendulous flowers in shades of red, yellow, orange, pink, or purple and fall into subgenus Bravoa. So, the distinction is really clear. Despite that, adding these subdivisions wouldn’t serve much benefit. Almost all observations on iNat can be identified to species with reasonable confidence, so including the two subgenera would provide little value and add needless complexity.
Overall, I’d say a minimum requirement is to have a valid, published subgeneric framework. But almost as important is that the divisions are useful for iNat identifiers, and that we can expect them to stay fairly stable (i.e. they’re based on strong phylogenetic evidence).