titanmelon said:
What's the difference between unknown_species and ambiguous_species?

I tried to make the distinction more obvious in each article, but not really sure if there's an agreed definition for either

Yep, those are fine. Unknown_species for ones that might be recognizable by someone, ambiguous_species for ones that are clearly ambiguous.

Both are low-priority tags, since they don't serve any purpose beyond being tagging aids (as far as I can tell).

titanmelon said:
So what tag should we use for plant humanoids?

...humanoid, plus whatever is the actual species (dryad and alraune are common examples). Plus the flora_fauna as a supplementary tag.