American taken by fresh flower's opening (8)
I believe the answer is:
aperture
'american taken by fresh flower's opening' is the definition.
'aperture' can be an answer for 'opening' (aperture is a kind of opening). I'm not certain of the 'american taken by fresh flower's' bit.
'american taken by fresh flower's opening' is the wordplay.
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'taken by' means one lot of letters go next to another.
'fresh' becomes 'pert' (I've seen this before).
'flower's opening' becomes 'ure' (I can't justify this - if you can you should believe this answer much more).
'a'+'pert'+'ure'='APERTURE'
Can you help me to learn more?
(Other definitions for aperture that I've seen before include "Opening, to let light enter a camera perhaps" , "Hole, gap" , "Crack" , "'Hole, opening (8)'" , "Opening through which light enters a camera" .)