Your mention is of Invitation Tags. I use a few of those to gather specific and useful Observations into projects. I leave a comment, (like Mark does for Galls and Plant Diseases), asking for the addition of a unique Tag. My seaweeds Project literally depends on them. https://www.ispotnature.org/communities/uk-and-ireland/view/project/777036/the-seaweeds-invitation-gallery
Galls are not unique in the way you explained, as both Plant Diseases and Seaweeds are in different and unrelated taxa. One wouldn’t be, if we had Algae as a Group - they could all be collected using the Habitat and Group designations. Or if everyone who adds a seaweed used the Tag Marine Alga.
Of interest is that the Curator can and might add or remove tags by ‘reasonable and reasoned’ request.
We should all be aware of the potential usefulness of the Tags taxonomy1 and absent1 see Taxonomy issues PLEASE