After you address zuzu's questions ...
Question about moderating: staying with the example of the Hibiscuses, zuzu is working on the tropical Hibs so she would be assigned H. rosa-sinensis and its children and so forth. I am working with the hardy Hibs, H. syriacus and H. moscheutos, because those are the only two hardy Hibs that have parent plant info thus far. So I would get whatever falls under those. But what about the other tropical and hardy Hib species? They don't get assigned a moderator until they have a Parent entry or how do you see that working?
As far as the Euphorbias, I would think take it out in the Parent Plants area (the single little databox entry) and leave Hibiscus as a general entry in the database so people have a place to upload their 'species unknown' photos.