Something from the florist, the ultimate in tulip arrangement for auntie (7)
I believe the answer is:
petunia
'something from the florist' is the definition.
'the ultimate in tulip arrangement for auntie' is the wordplay.
'the ultimate in' suggests the final letters.
'arrangement for' indicates an anagram (I've seen this in other clues).
The last letter of 'tulip' is 'p'.
'auntie' with letters rearranged gives 'etunia'.
'p'+'etunia'='PETUNIA'
(Other definitions for petunia that I've seen before include "Garden plant, originally from S. America" , "Plant cultivated for its white, pink, blue or purple funnel-shaped flowers" , "Flowering plant" , "Colourful" , "Flower - tuna pie (anag)" .)