Flower's lower rim split by tip of stamen (7)
I believe the answer is:
cowslip
'flower's' is the definition.
(thesaurus)
'lower rim split by tip of stamen' is the wordplay.
'lower' becomes 'cow'.
'rim' becomes 'lip' ('lip' can be a synonym of 'rim').
'split by' is an insertion indicator.
'tip of' suggests taking the first letters.
The initial letter of 'stamen' is 's'.
'cow'+'lip'='cowlip'
'cowlip' going around 's' is 'COWSLIP'.
(Other definitions for cowslip that I've seen before include "Early spring flower" , "Type of primrose" , "Yellow wild flower" , "Yellow field flower" , "Wild spring flower" .)