National flower of Mexico (6)
I believe the answer is:
dahlia
'national flower of mexico' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dahlia that I've seen before include "Peculiar Ali had this flower" , "Brightly coloured garden flower with tuberous roots" , "Flower, often ball-shaped" , "Ali had (anag) - showy flower" , "Flower named after a Swedish botanist, d. 1789" .)