You might try posting this in https://forum.inaturalist.org/t/city-nature-challenge-2026/77622 for more responses. (Mods, as appropriate, please move the comment I’m responding to and this response to that thread…I want to respond, so I just have it do it here for now. Sorry - thanks.)
From my perspective -
(1) if there are multiple photos of what appear to be the same plant, many identifiers will comment that the observation(s) are duplicate, and encourage the observer to combine them into one observation. This doesn’t always work though because the observer may have already ditched the platform. If the photos linger as duplicates, ID’g them at least removes them from needing ID.
(2) (a)if a plant is clearly in an area where cultivated plants would occur (e.g. a botanical garden, someone’s backyard), don’t hesitate to mark it as cultivated.
(2)(b) re: your question about certain species - sometimes, if you ID a plant to genus or species, the observation will automatically default to “cultivated” if more than a certain percentage of that species or genus is “cultivated” in iNat’s system for the geographic area. Roses are a great example of this.
(2)(c) you can always ask, but that often doesn’t yield an answer.