Plant circle around which mad girl frolics (8)
I believe the answer is:
marigold
'plant' is the definition.
(marigold is a kind of plant)
'circle around which mad girl frolics' is the wordplay.
'circle' becomes 'O' (O is a circle).
'around which' means one lot of letters goes inside another.
'frolics' indicates anagramming the letters (I've seen 'frolic' mean this).
'mad'+'girl'='madgirl'
'madgirl' anagrammed gives 'marigld'.
'o' put inside 'marigld' is 'MARIGOLD'.
(Other definitions for marigold that I've seen before include "Orange daisy" , "floral item" , "Garden plant of the daisy family" , "Yellow or orange flower" , "Flower - grim load (anag)" .)