I don’t see why it matters that the photo is of multiple flowers that have been staged rather than multiple plants in situ. If someone uploaded an observation with a photo showing specimens of different species next to each other for comparison purposes, it would not be an invalid observation, provided the choice of subject is established and the observation info reflects this.
Is it ideal to have different specimens of (potentially) different species in an observation with no indication in the observation notes or the photo which one is intended? No, of course not. But this doesn’t mean it should be treated as defective merely because the intended subject is ambiguous.
If the observer is mistaken about all the flowers being identifiable as the same species, this can be noted. In fact, communicating the identification challenges to the observer is generally a good course of action, as would communicating to them why they should choose one specimen as their focus.
If there is reason to believe that the individual flowers are not from the same location or harvested at the same time, and the observer is not willing to indicate which one should serve as the focus, the DQA for “location accurate” or “date accurate” can presumably be used.
If the date and location reflect where the flowers were photographed rather than where they were seen, the DQA “captive/cultivated” or “location accurate/date accurate” can be used.