Unsafe flowers for rabbits is a big concern considering some (like many other things) are poisonous and could even be deadly. Here is a list of some of the unsafe flowers for rabbits:
Lily of the Valley
as well as any bulbs
There most likely is other unsafe flowers for rabbits that aren't mentioned in this list. If you have any concerns what is safe or unsafe, please comment on this post.
Have a look at this link about caring for your rabbit