Here's a great little video from Dr Markus Eichhorn, an ecologist at the University of Nottingham, pointing out some of the horticultural blunders in the Harry Potter movies.
I've seen none of the Harry Potter movies (Hah!) so can't add more.
But I once started keeping a record of all the plants I'd spotted on far and distant planets visited on Star Trek. I began when Captain Picard, I think it was, beamed down into a large field of argyranthemums (marguerites), of all things, and another episode found Captain Kirk and his crew slashing their way through a forest of garden centre sized date palms.
But the truth is I just couldn't face watching every episode of Deep Space Nine on the off-chance of spotting a begonia.