Platform heel of trendy plant (5)
I believe the answer is:
daisy
'plant' is the definition.
(daisy is a kind of plant)
'platform heel of trendy' is the wordplay.
'platform' becomes 'dais' (dais is a kind of platform).
'heel of' suggests the final letters (in a down clue, the letter at the bottom).
The last letter of 'trendy' is 'y'.
'dais'+'y'='DAISY'
(Other definitions for daisy that I've seen before include "Grassland flower" , "chain, just the smallest bit?" , "Plant; girl's name" , "girl" , "Lawn flower, weed" .)