Merging vs. swapping when facing incomplete information about synonymy

A common situation I’ve noticed in starting to curate vascular plant taxa here:

First, authority_W described taxon_A.
Then, authority_X described taxon_B, without referring to authority_W’s taxon_A.
Later, authority_Y listed taxon_B as a synonym of taxon_A. Authority_Y referred to authority_Z’s checklist to justify this synonymy.

We use authority_Y as a standard taxonomic authority on iNaturalist. But when I check Authority Z’s checklist, I see that it gives neither a rationale nor a citation for the synonymy decision, merely listing taxon_B under the heading “synonymy” for their entry on taxon_A.

This leaves me to wonder whether this change means:

  1. An expansion of the concept of taxon_A (becoming taxon_A’) to include taxon_B, which was, in fact, different in some (apparently minor) way from taxon_A.

  2. A decision that taxon_B is best understood as an exact (fully redundant) synonym of taxon_A.

  3. Some other relationship between taxon_A, taxon_A’, and taxon_B.

This ambiguity can be prevented by using <,>, ≡ signs, or words like “homotypic” and “heterotypic”, (and other phrasings in zoological lit), but I rarely see this.

My impression from reading the curator guide is that:

For situations like (1) we should use “taxon merge”, because this instantiates a taxon_A’ to replace taxon_A.
For situations like (2) we should use “taxon swap”.

But what should we do when it’s not clear whether (1) or (2) is the case?

…Or it is recommended that for both situations (1) and (2) we should use “taxon swap”, saving “taxon merge” for other, more complex changes?

It’s my understanding that the merge tool is simply a more efficient way to do a swap where you know you have several inputs and one output. But I could be wrong.


The biggest difference I see is that the merge tool creates a new taxon concept, whereas the swap tool keeps the old one (and fills it with more observations). This is a weird use of the word “swap” imho.

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definitely confusing phrasing to me too


As I understand them, neither kind of change necessarily creates a new taxon concept, but both can be used to do so. It all depends on what the input and output taxa are for either kind. One can only create a new taxon concept by first creating a new taxon, then using it as the output in taxon change.

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