I know this is a very late reply to your topic, but after I read what pleary says here
I find using unobserved_by_user_id= in conjunction with lrank=species gets the “correct” results on the species tab. So
https://www.inaturalist.org/observations?place_id=2738&unobserved_by_user_id=arboretum_amy&view=species&iconic_taxa=Plantae seems to imply I haven’t seen Isocoma menziesii because I haven’t seen a subspecies, but
https://www.inaturalist.org/observations?lrank=species&place_id=2738&unobserved_by_user_id=arboretum_amy&view=species&iconic_taxa=Plantae removes Isocoma menziesii from the view.
Now if all Isocoma menziesii observations in this place were identified to subspecies, perhaps that would become problematic, but I don’t think it’s likely to happen.