Just ask a series of questions:
- Is it a plant or animal?
- How large is it?
- Where are you (location permission)
- Does it have green leaves?
- Does it have woody stems?
- Does it have whorled or alternate leaves? (Show images)
- Does it have yellow flowers?
This is how a lot of field guide books work, but they require a lot of flipping back and forth, scanning tables of contents, and memorizing terminology. An app could just be tap-tap-tap-tap-tap, drilling down very quickly and showing images at every step.
The "only" difficulty is getting the database of attributes - maybe it already exists. Maybe an app like this already exists and I haven't been able to find it?
Thing is, the series your questions you show are easy to answer but they don't get you any further than halfway. Problem is in the questions you do not show: there it starts going into details, terminolgy starts to matter (seriously, if you've never read those words it's like a foreign language) and differences become hard to spot. Part of this could perhaps be alleviated with pictures but I doubt it; I've seen websites attempt it but none were really good and they all did a subset of plants. Probably because it's quite the amount of work to do them all, even for a region.