Conventions for Scientific Name Synonyms: 1-1 vs. "Contained Within" vs. "Overlap" Relationships

Nature Talk
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This post is primarily about plants but the question is general and may be relevant to other kingdoms too.

I sometimes find particularly taxa of plants that are a mess due to tons of taxonomic changes and/or alternate names, with different sources using different naming schemes, and I rely on a lot of external resources, especially POWO, and also USDA and BONAP, to make sense of them, matching up what refers to what.

An example would be the Nuphar genus. Some authorities have considered there to be only a single species in that genus, typically Nuphar lutea, and then they consider the different populations of it to be subspecies. Nowadays, most authorities consider the different populations to be different species, typically 8, but there are as many as 84 different species names in the genus that have been proposed by different authors. And if you check five different sources, you might find five diferent naming schemes, and it becomes really confusing to know what population(s) a particular text is referring to.

So for instance where I live in the Mid-Atlantic US, the species currently recognized by POWO is Nuphar advena (Aiton) W.T.Aiton.

On POWO, under “Synonyms”, for this species/authority combo, they list a whopping 34 “synonyms”; here is a selection of them:

  • Nuphar lutea subsp. advena (Aiton) J.T.Kartesz & Gandhi
  • Nuphar lutea subsp. macrophylla (Small) Beal
  • Nuphar lutea subsp. ozarkana (G.S.Mill. & Standl.) Beal
  • Nymphaea ozarkana G.S.Mill. & Standl.

It’s not clear from these “synonyms” if they refer to the same total populations. Upon close examination, in most cases, they do not. So they’re not really synonyms (i.e. not having the same or nearly the same meaning, not really referring to the exact same taxon) even though they’re listed as such.

For example, there is a “contained within” relationship between Nuphar advena (Aiton) W.T.Aiton and, say, Nuphar lutea subsp. ozarkana (G.S.Mill. & Standl.) Beal., in that Nuphar lutea subsp. ozarkana (G.S.Mill. & Standl.) Beal. refers to a small subset of the population of Nuphar advena (Aiton) W.T.Aiton.

As a different example, there seems to be a one-to-one relationship between the names Nuphar lutea subsp. ozarkana (G.S.Mill. & Standl.) Beal and Nuphar ozarkana (G.S.Mill. & Standl.) Standl. But POWO provides no clue as to this relationship; instead, it just points each of these to the same taxon.

Clarifying these relationships is relevant to me because I often work with range maps and other documents that refer to species, subspecies, and varieties, and I want to know what they’re referring to and I want references that help me to understand which terms correspond to what.

POWO, along with most other taxonomic authorities I’ve consulted, ones that have lists of synynoms, such as ITIS, and USDA, don’t seem to make the distinction between 1-1 relationships and “contained within” relationships.

Furthermore, it gets even uglier / more complex. There are some situations where names are listed as synonyms where there doesn’t even seem to be a clear “contained within” relationship. For example a species name proposed by one author, might be broken up and lumped in with different species, but none of these portions covers the full range of the other species. So what is listed as a “synonym” is simply a “non-empty intersection” or “overlap” between the populations referred to by the name.

It Gets Still Worse

Probably the worst thing ever is that the same name+authority combo doesn’t even refer to the same population. For example, POWO now lists the name Nuphar lutea (L.) Sm. as referring to populations extending only from Europe into Asia and barely into North Africa. But the USDA refers to the same name and authority, Nuphar lutea (L.) Sm., with the “old” convention, before the North American populations were broken out into separate species.

So like, when a source or reference cites “Nuphar lutea (L.) Sm.”, it’s not even possible for me to know what classification scheme they’re using. I thought the purpose of including the authority was to know what classification scheme was being used, so that the name was unambiguous? But the name “Nuphar lutea (L.) Sm.” is now ambiguous, because people aren’t recording the authority of the authority that broke apart the species as a taxonomic change to the species that was broken apart. I don’t know if this is convention (if it is, it’s contrary to the whole purpose of the convention of citing naming authorities) or if it’s an error, like perhaps POWO or perhaps USDA has wrongly cited the authorit in this case? But it’s enough to be a huge headache.

It would be highly relevant when looking at lists of scientific synonyms to know which of them represent one-to-one relationships, which represent “contained within” relationships (and in these cases which direction the relationship goes), and which represent “overlap” relationships where neither population referred to by one name is contained within the other.

This stuff is a high priority for me because these complex relationships are the norm, rather than the exception. There are also many examples of 1-1 relationships which are simple to resolve, and many “contained within ones”. There are fewer “overlap” scenarios, but they tend to be highly problematic so it is important to know when you are dealing with those.

So my questions here are:

  • Are there any conventions for notating the distinction between 1-1, “contained within”, and “overlap” relationships when noting scientific “synonyms”? Surely there are different words that we could use to refer to these types of relationships.
  • Why are so many authorities listing things as “synonyms” that aren’t really strictly synonyms? I thought scientific language was intended to be precise, and many aspects of systematics and taxonomy go to great lengths to do so, yet people seem to be using the word “synonym” extremely sloppily and carelessly, to the point of great imprecision, loss of information, and confusion.
  • Are there any databases or other resources that can help me make sense of this stuff, and classify a “synonym” as having a particular relationship type, and here’s the kicker, without having to do a deep-dive into the primary literature and/or analysis of secondary references like actually comparing range maps? I can figure this stuff out, it’s just awfully time-consuming and error-prone.
  • In the absence of a “nice” solution like those above, is there some way for me to logically deduce these relationships through public data available in places like POWO, ITIS, perhaps other places I am not checking? Perhaps IPNI that POWO uses as a source for their data?

It’s like, the people who do all the wrangling of these scientific names already know all this stuff about the relationships, they just aren’t notating it clearly in references like POWO that list scientific synonyms. Are these people writing down and storing this information somewhere else, in a public database where I can look it up? Or is the information just getting lost, like they just keep it in their heads and then sloppily write everything down as a “synonym”?

The closest I’ve found to this is the BONAP nomenclator, which often has a list of which species and subspecies have been lumped into which species and subspecies under a taxonomic reclassification, but it is hardly comprehensive, and it also doesn’t list authorities which makes it borderline unusable in some of the messiest cases (and this is where I would most need it), and I’ve also found a ton of cases where the relationships it lists, including the authorities that it uses (which you can look up in their TDC=taxonomic data center), overtly conflict with what I find listed in POWO and I find myself unable to make sense of the whole mess. Like BONAP’s nomenclator pretty much only lists entries for the transition between the USDA PLANTS database’s naming scheme and BONAP’s naming scheme, which sometimes corresponds to POWO’s scheme but often does not. So, while helpful in some cases, its usefulness is limited.

I would be grateful for any insights anyone has to offer!

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Hi Cazort,

I feel your pain!

Unfortunately, the way we use the concept of synonymy in taxonomic nomenclature is coarse, and there is no formal way to distinguish among the many different ways two names can be synonyms. As you’ve correctly pointed out, all manner of splitting, lumping, nesting and more complex reorganizations are all hidden under the same word.

In general there isn’t a good solution. However, a group of US botanists have made some efforts to provide expanded nomenclature to more explicitly capture the different kinds of synonymy that we encounter. This may even be directly useful for you, since one of the leading proponents is Alan Weakley, author of the Flora of the SE USA. It’s available free to download (after registering), and uses an expanded synonymy concept that goes a long way to address this issue.

Here’s his explanation, copied from an earlier draft:

Prior to the name cited, a symbol is inserted to convey the conceptual relationship of the
two names – in other words, the relationship of the name and associated taxonomic concept being applied in the Flora to the name and associated taxonomic concept in the other references, regardless of the nomenclatural relationship of the two names. “=” means that the two concepts are believed to be identical. If the taxonomic concept is identical and the name is also the same, the name is omitted. “<” means that the name in use in the flora is finer than (a split relative to, and wholly included within ) the name as used in the reference(s) listed. “>” means that the name and associated taxonomic concept in use in the Flora is broader than (a lump relative to, and wholly including) the name as used in the reference(s) listed. “><” means that there is a complex and cross-cutting relationship between the name and associated taxonomic concept used in the Flora and the name and associated taxonomic concept used in the reference(s) listed. “?” means that the relationship between the taxonomic concepts is not understood by me at this time (often this means that there are complications outside the flora area, and often outside of North America, that make the concept relationship difficult to determine).

Alan’s approach doesn’t resolve all the problems you’ve encountered, but it’s a solid start. And it likely includes most or all of the species in your area, as it covers northern Florida north to southern New Jersey.

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Thanks so much for pointing this out about Weakley’s flora!

That book is one of my core sources that I’ve already been consulting for a variety of purposes, but for some reason I missed that detail in it! That system is absolutely beautiful, exactly what I have been looking for, and although it only covers part of the US, it’s a part that is particularly high in biodiversity so this is going to cover a large portion of the issues I’ve been having.

Now I need to figure out something equivalent that covers the Western US. The other areas that I’ve been having the most problems with this stuff is the southwestern desert areas, rocky mountains, and California.

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I also found this piece:

https://www.napier.ac.uk/~/media/worktribe/output-255552/scientific-names-are-ambiguous-as-identifiers-for-biological-taxa-their-context-and.pdf

which makes the compelling point that the convention for scientific names is inadequate for describing a taxon unambiguously, that in addition to referencing the original naming authority, you need to also reference an authority for the taxonomic context or scheme being used.

This practice, unfortunately, does not seem to be the norm, and I can’t even seem to find a single authority that follows it. However after encountering these problems and reading this piece, I am solidly convinced that the points this author makes are correct and I am wanting to jump wholeheartedly onto this proposal and help to normalize the practice of citing an authority for taxonomic context when specifying scientific names, as it seems like it would more-or-less solve the second problem above (i.e. the problem that a scientific name + naming authority can still be ambiguous.)

I’m curious how many people are aware of these issues and this sort of proposal to address it, and how far along people are towards implementing or normalizing a practice like this?

Frankly it strikes me as bizarre that it’s 2022 and we still have all the major authorities not doing it this way.

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Thanks for this, @plantarum! I had seen Weakley’s notation but never figured it out. Very helpful.

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That’s what I thought too; this past week has been a rude awakening to just how messy (if not broken) the state of plant taxonomy (and perhaps all taxonomy) is.

What I am finding is that in mainstream usage, including in POWO, but for the most part, in nearly all sources I check (Weakley’s Flora and BONAP’s nomenclator being the only two exceptions I’ve found), “synonym” does not mean this, and the term “synonym” is used broadly to include any and all cases in which there is some overlap in the populations referred to by the two terms.

A substantial portion of these are true synonyms, but a large (perhaps larger) portion of them are “contained within” relationships, such as the relationship between a subspecies, variety, or other sub-population and the broader taxon or population. Furthermore, a small but important subset of them are messier “intersection”-type relationships where the taxon or populations referenced by each term are not contained within the other, not in either direction, but rather, there is partial overlap but there are also subsets referred to by each name that are not intersecting with those referred to by the other.

And, outside of Weakley and the BONAP nomenclator, it seems no one is noting or distinguishing the nature of these relationships, they’re all just lumped into generic lists of “synonyms”. Including by bodies and in databases specifically intended to compile and present synonyms, such as ITIS and IPNI. (Unless I’m missing something and this data is there and I just don’t know how to access and/or interpret it? Please, someone, I desperately want to be wrong here.)

And as if this isn’t enough, often the name itself is ambiguous. This sort of thing is exceptionally common, it happens pretty much whenever a species is broken up in such a way that one population retains the original name, which I think may be mandated by most naming schemes because preference is given to the oldest name describing a particular taxon. Like in example I gave above, the ambiguous name would be Nuphar lutea (L.) Sm., which is ambiguous in that it could refer to the old scheme that considered it a single species covering the entire northern hemisphere, or the newer scheme that considers it to only refer to one of eight species, the one found roughly from Europe through Siberia.

Just referencing the naming authority is insufficient to make the name unambiguous. What is needed is an authority for a taxonomic context, such as a flora for a region in question, a global flora, or a flora large enough to cover any relevant taxa. So for example, Weakley has a list on page 13 of his FSUS book, of the authorities he uses, and when a name is ambiguous he not only refers to the naming authority, but also the authority of the taxonomic context, which mostly includes larger flora manuals like his own.

But this is not the norm. The norm is not to specify a taxonomic context and thus to have the potential of an ambiguous name. And there are a large number of such names and it is hardly clear-cut to find out exactly when you are dealing with such a name.

The fact that anyone thinks such a system is acceptable, let alone good, is utterly bizarre to me. I thought the whole point of scientific names and referencing authorities for each name, was to remove the ambiguity? But the ambiguity is there and I’m not seeing any major organization getting on board with a way to address these problems.

It is highly disturbing to me, almost like I started asking some small questions and I’m starting to feel like one of the basic underpinnings of biological science is seeming fundamentally broken, and like no one is acknowledging it or taking responsibility to fix it.

Like, we have revised the consensus conventions for scientific names how many times, and this issue still has not been addressed?

I feel like my brain is going to explode.

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For animal taxonomy, I’ve seen the term synonym used in slightly different ways. The synonym might be a one-to-one equivalent of the current name and is either an alternative name that some still use or it is no longer in use … OR or it might refer to other names applied to the organism at the subspecies level which might or might not be currently recognized. If you look at a chronological synonymy of a vertebrate species, you’ll see various names that were applied at the species or subspecies level for the currently recognized species and some may be in use as subspecies and some will be junior synonyms for the species or possibly a subspecies and that are not in current use. I believe with plants the authority notation is a lot more complicated than what is used for animals where you’ll only see one author (or set of authors) for a new name, the original describer(s).

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I re-read my previous message and not sure that makes sense even to me.

To address one of your questions, I have seen used in a synonymy the notation “(in part)” after a name to indicate that that name does not directly correspond to the taxon as currently understood … it only applied to some populations.

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This might or might not help…

Every (valid) scientific name is merely a label attached to a single type specimen in a museum or other repository somewhere in the world.

Any time two or more type specimens are decided to belong to the same species or other taxon, the oldest available name attached to any of those type specimens must be used as the name of that collective taxon.

This is why the same name published by the same author can refer to different taxonomic concepts. A taxon with that name always includes the type specimen to which that name was originally attached. But beyond that, the name can refer to any number of taxonomic concepts, depending on which other type specimens (with younger names) are considered to belong to the same taxon as the name-bearing type specimen.

The “long-hand” way to unambiguously say what is meant by application of a particular name is to list the names of all other included type specimens as “synonyms” under the accepted name. This is what POWO tries to do, and what all rigorous taxonomic publications generally try to do.

A big exception is large compilations like regional or continental floras (just focusing on plants for the moment), where exhaustive lists of synonyms would make the volume(s) impossibly large. That is when authors resort to citing only selected synonyms that help clarify the taxonomic concept, and/or develop symbolic systems like the one @plantarum pointed out above.

The root of the mess, of course, is that data supporting which type specimens do and do not belong to the same taxon increase and generally improve over time, and the meaning of the name applied to that taxon then also changes. (Sometimes the name itself changes when an older type specimen becomes included in the concept.)

Then adding to the mess is when incomplete or ambiguous data allow room for competing hypotheses about which type specimens do and do not belong to the same taxon. (Not to mention, at which taxonomic rank that taxon should be accepted.)

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I’m not a botanist but I did purchase a volume of Flora Neomexicana, published in 2020, for my state’s plant species. Includes an annotated checklist of recognized species and varieties and a whole lot of synonyms for any form that has them. It’s really a remarkable body of work. I haven’t cross-checked it much with the taxonomy in INat so haven’t encountered any major discrepancies yet. Wonder how many states in US have such a publication?

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Let’s keep this in perspective. Taxonomists know how to deal with these issues. They have to in order to do their jobs. The science isn’t fundamentally broken. Be we are doing a poor job of communicating some important aspects of taxonomic relationships. And to be honest, it would make our own jobs easier as well.

I saw Weakley present his system in a talk when I was a grad student, 15 years or so ago. At first I didn’t understand why it was needed. As a taxonomic researcher, untangling all these different kinds of synonymy is a basic part of the job. Once you’ve done it enough, it’s easy to forget that it doesn’t have to be this hard. I suspect that’s why this hasn’t seen wider uptake: the people best placed to do so already know how to deal with the issue for themselves.

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This makes sense.

But is this really unambiguous? Like in the situation where you have a name B, which gets split up into names A and C (Look to the Oenothera genus for a lot of examples of such reclassification), there are many different possible classification schemes for breaking up B into subspecies. Some schemes may recognize the validity of some subspecies names, but not others. Furthermore, the different schemes might have different diagnostic criteria for how to lump individuals into one subspecies vs. the other, and thus, even if you have two different authorities that recognize the same set of subspecies names and same type specimens, they might be referring to different populations with these names.

If there were no differences in classification schemes, in this scenario, it would be fine. You could look through all the names for subspecies, and then see which ones are listed, and know.

But…with the status quo, am I correct that, looking at the list of synonyms itself is insufficient for unambiguously specifying exactly what is and isn’t referred to in the taxon in question?

At a bare minimum, it would be necessary to check proposed subspecies of the split taxa, and then see which names the authority accepts vs. rejects. So it is not possible “in one record” to know what the name refers to, i.e. you would need to look to the overall context, so the name becomes a bit ill-defined and self-referential. Like the whole system of referring to type species is to make the system objective. It’s not clear to me how this is any more objective or rigorous than Weakley’s system of referencing regional flora as taxonomic context.

But furthermore, I am not sure that this alone (checking lists of accepted/rejected names of split taxa whose subspecies are listed as synonyms of the taxon in question) is sufficient to make the taxon name unambiguous, because even with the same subset of names there can be disagreement about what is being referred to. To me, the system Weakley uses seems more unambiguous and more objective, whereas the system of just listing synonyms seems to have more problems with ambiguity.

Please correct me if there is something I am missing here.

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The issues I’m having here are not so much iNaturalist problems, which is why I posted in “Nature Talk” and not “General”.

These problems arise mainly when I am trying to reference multiple sources. For example, I frequently consult plant range maps, notably the county-level maps of BONAP and USDA PLANTS, when trying to ID plants and looking over records towards the end of plant ranges.

However, iNaturalist generally uses POWO’s classification scheme, which doesn’t always correspond to the scheme used by the USDA or BONAP. USDA and BONAP are different, with differences clarified in the BONAP Nomenclator, but I have found that the combination of synonyms listed in POWO and the BONAP Nomenclator, in a few cases, is inadequate for sorting out the mess.

I would welcome this addition, and it might be helpful to people who are not aware that iNaturalist generally uses POWO’s classification scheme, and are struggling to make sense with names that don’t correspond to what they might see on a site like USDA or BONAP, in the cases where they disagree. However I don’t think it would be sufficient to address these problems.

My problem is that I am having a tough time proceeding when I see differences in how different sources have treated certain taxa.

It’s particularly problematic when I’m looking at sites that, unlike POWO and other taxonomic authorities, and unlike Weakley’s flora, don’t clarify a taxonomic context.

But even with POWO I am having some trouble making sense of some ugly and complex situations.

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Maybe part of my problem is that I’m not experienced with this sort of wrangling, and thus, I lack the skills to sort out inconsistencies when they do arise. I definitely agree here:

Like it seems like clarification and improvement of this stuff could have a whole bunch of sweeping benefits. And, any time you make someone’s job easier, you free up resources for them to do more.

At a bare minimum I think the terminology (particularly “synonym”) and way the information is presented is misleading, and could be improved. Sites like USDA, BONAP, and POWO are used by people far less knowledgeable in plant taxonomy than someone such as myself, and I am clearly far less knowledgeable than some of the people in this thread.

So I’d imagine that a lot of other people are having these problems, and for every one person like me who speaks out about it, there are probably 10 others who suffer in silence, and 100 others who simply give up before trying because the system seems intimidating.

Like I can’t help but wonder if the opacity and other problematic aspects of this system is a factor in why the nursery industry and horticulture in general has been slow to keep up with modern taxonomic changes. It’s like, why even try if the system is so complex as to be hard to understand, while at the same time still failing to deliver the unambiguity that you would hope it to?

This is an interesting insight and I think I can understand and relate. Like I have been designing interactive websites for 13+ years, but because I design them, I know how to use the sites I design, so when it enters the testing and use phase, I often get a lot of feedback about stuff that seemed intuitive to me, that is not intuitive to the users who did not design the system. If I don’t consider and respond to and address this feedback, the sites fail to reach a big audience and never get the sort of engagement I had intended. This is one reason why the first major interactive site I launched was a bit of a flop.

I would like to get better at figuring out how to work within and understand established practices, particularly, how to make sense of the really messy taxa that I am currently struggling with, but I would also like to find a way to present the same information and relationships to a general audience in a way that is more intuitive.

And if there is (as I suspect there is, in at least a few cases) true ambiguity in the status quo, I would like to remove it by specifying a taxonomic context the way Weakley does and/or the way is proposed by those three researchers at Napier university. (I have emailed all of them and am curious if I am going to get a reply! I would be curious to see if anyone has implemented or further developed their ideas because they seem super promising and like they would probably solve these problems in a graceful and thorough way.)

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For animal taxa, I’ve sometimes had to do a deep dive into the older scientific literature to trace the path of certain names – what was the distribution of the originally described taxon, what synonyms have been proposed over the years, how the concept of the currently recognized taxon has changed, etc. It can be fun but also frustrating if you can’t access the sources or if the situation is particularly complex. Thankfully in many of these cases, more modern taxonomists have already grappled with the taxonomy and come up with good reviews that save me some work.

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Yeah, this all makes sense. I actually still prefer POWO’s taxonomy scheme, it seems “best” in a long list of ways, like most up-to-date, resolving the most inconsistencies.

My issues here are mainly that the presentation of their scheme seems a bit opaque to me, and it makes me do more work than I would like to have to do, to figure out the information that I want. In particular, it’s very hard for me to make sense of how someone else’s scheme relates to theirs, when they don’t line up.

And for this reason, I wish I had more information when they list “synonyms”. I wish I had a reference to some sort of authority beyond just the naming authority, an authority for taxonomic context.

Like, I just flat-out don’t know how to use POWO (or if it is even possible to use it, i.e. if the information is even in there) to resolve questions like, if I type in a scientific name of a taxon that has been split into different taxa, POWO just points me to the taxon that the type specimen has been assigned to, without giving me any indication that there has been a split.

Like an example, say I type in Oenothera parviflora L… They just take me to a page on that taxon, saying it’s an accepted name. They do not note anywhere that Oenothera parviflora var. muricata (L.) Farw. is an accepted synonym of Oenothera biennis L. Similarly, if I type in Onagra chrysantha, they say it’s a synonym of Oenothera parviflora L. and redirect me there. But they don’t tell me that Onagra chrysantha var. latifolia Spach is a synonym of Oenothera biennis L. I only can see these by looking over the record for Oenothera biennis L. I’m pretty sure there is no way to figure this information out from POWO alone, but I can get some of it by going to its source, INPI.

At IPNI if I type in Oenothera parviflora, and then look through that list and see the 7 entries of subspecies and varieties, and click all 7 links to POWO, I can see what they redirect to. This yields records that point to 4 different accepted taxa: Oenothera oakesiana (A.Gray) J.W.Robbins ex S.Watson, Oenothera parviflora L., Oenothera villosa subsp. villosa, and Oenothera biennis L.

Three of these are species, but one of them is a subspecies.

But the thing is…there is so much information loss from the actual relationships. The fact that one record “points to” the species does not mean that it refers to the whole of the species. Each of these old names referred to something, some population of plants. And it’s not clear from how this stuff is presented, how to get that information, of the information even exists in INPI at all.

And yet having that information is critical if you’re reading a source that refers to a population of plants by one of these old names, and you want to know what it is talking about, i.e. what the scope of the material presented is, what population(s) of plants it applies to.

Clearly, the people who compiled the data underlying POWO have done immense amounts of work to figure out all these relationships and then record something about them. But it seems that the information they are presenting to the world is a tiny fraction of the information that they have reviewed, so like…why go through all this effort and then present such a “reduced” form of information to the public, if that makes sense?

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Isn’t this where a local Flora publication – if there is one available from your area – come into play, in conjunction with other global sources such as POWO? For a wide-ranging species that occurs in your region of interest, it would seem that not all names including synonyms that have been proposed for the taxon would be applicable to the populations in your area and potentially could be disregarded. For my state Flora publication, I’m not sure they addressed all names that have been proposed for a particular species but only those that have been used in reference to populations that occur in my state. Synonyms that have been applied to populations in, say, Europe might not be relevant (unless of course they affected the taxonomy of the organism rangewide).

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This is an easy problem to solve, and it’s not the core problem I’m having.

My problem is, when there are relevant “synonyms” that refer to populations in my area, figuring out how they are related to the new accepted taxa.

Like, when I look up a range map on USDA or BONAP, and it corresponds to a subspecies or species on POWO that has been split up, how to make sense of it? Like it’s frequent where I see a range map on one of these other sites, then POWO redirects that scientific name to a different name, but when I check the POWO range map, the range is wildly different from the reported range for the “synonym” on USDA or BONAP. It’s common that the range is much larger or much smaller, and in some cases it is both, i.e. there is partial intersection but no containment either way. And in a few cases, there isn’t even any intersection at all.

And it’s further complicated by the fact that there can be genuine disagreement about the presence or absence of certain plants in certain regions. BONAP is usually good at noting records that it marks as dubious or erroneous. POWO doesn’t notate this. So…when I glance at a map and the range maps don’t jive, sometimes it’s not even clear whether I’m dealing with a difference in taxonomic classification, vs. a dispute about the range of an agreed-upon taxon. And of course, there are cases where both apply.

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Not unique to plants. Molecular systematics has jumbled up many taxa and I no longer know the distributions or applicable names for a number of organisms that I was and am familiar with. It doesn’t keep me awake at night. I view our current understanding of systematics as a period of great flux and the resultant taxonomy is gonna be a bit of a mess. Maybe it will help keep my old brain working for the coming years.

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jdmore basically sums it up. A name is only really attached to one type specimen and different people may associate other specimens with that type specimen, sometimes in very different ways. Other types specimens that are included with the one with precedent, become synonyms whether they are equal or part of. “In part” can only refer to a particular person’s treatment as the type specimen of a name can only be lumped with one other active name. You refer to a particular treatment by adding sensu and the author of the treatment, perhaps with the date to remove ambiguity. I’ll lay out a relative simple example.

Malacothamnus palmeri sensu Kearney (1955) includes three varieties he recognized: palmeri, involucratus, and lucianus.

M. palmeri sensu Munz and Keck (1963) includes two varieties they recognized: palmeri and involucratus. They say lucianus is intermediate rather than a synonym of either.

M. palmeri sensu Bates (1993 and 2015) only recognizes one species with no varieties and has lucianus and involucratus as synonyms of palmeri.

M. palmeri sensu Slotta (2004 and 2012) like Munz and Keck, Slotta recognized the two varieties palmeri and involucratus but, instead of considering lucianus an intermediate, lucianus is treated as a synonym of variety palmeri.

M. palmeri sensu Morse (2021) raised involucratus and lucianus to the species rank, so they are not included as synonyms of palmeri.

M. palmeri sensu POWO (2022) suddenly goes back to 1955 and recognizes the three varieties palmeri, involucratus, and lucianus, while retaining most of the remaining Malacothamnus taxonomy from 1993. Yep, POWO has issues, like most other databases.

Throughout all these changes, some specimens of what are now considered M. palmeri were included in what is now M. involucratus. So, even when both were recognized, the boundaries between them were drawn differently by different authors.

This is one fairly simple example and I ignored everything before 1955 when there were other genera involved. Doing your own literature review or finding one that someone else has already done in a journal article is pretty much the only way to get good answers and there may actually be no clear answers at all in some cases. It would be awesome if someone pulled together a giant taxon crosswalk database that included how people drew the lines between taxa and not just how the names changed, but that is a huge undertaking and could possibly take a 100 years or so to actually populate with all the data. Bottom-line, there are a lot of errors in treatments and databases, and different authors draw taxon boundaries different sometimes. Synonyms are messy. Unless you cite a particular treatment of a taxon and not just the author(s) of the taxon itself, there could be ambiguity. Even then, there will likely be ambiguity in a lot of cases.

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