It's a tricky one. An attractive woman probably has her fair share of approaches, and it;s difficutl to separate the genuine from the leery ones. The idea of flowers with your number is nice, but sadly, she is unlikely to respond - you may have noticed her, but, however genuine and nice you are, unless you stand out physically in a Depp / Clooney/ Beckham type way, she may not have noticed you back.
However, she may just be intrgiued enough to follow up your gesture, and you;ve nothing to loose, so I'd go for it.