Plant anything but a girl's best friend? (8)

I believe the answer is:

shamrock

I'm a little stuck... Click here to teach me more about this clue!

'plant' is the definition.
(shamrock is a kind of plant)

I can't explain the rest of the clue.

(Other definitions for shamrock that I've seen before include "Irish national emblem" , "Symbol of Ireland" , "Mash cork into the emblem" , "Native Irish trefoil" , "Ireland's special trefoil" .)

I've seen this clue in The Sun.

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