Flower alone did blend nitrogen (9)
I believe the answer is:
dandelion
'flower' is the definition.
(thesaurus)
'alone did blend nitrogen' is the wordplay.
'blend' is an anagram indicator (I've seen 'blended' mean this).
'nitrogen' becomes 'N' (N is the chemical symbol for nitrogen).
'alone'+'did'='alonedid'
'alonedid' anagrammed gives 'dandelio'.
'dandelio'+'n'='DANDELION'
(Other definitions for dandelion that I've seen before include "Flower with a "clock"" , "Common yellow-flowered plant" , "Yellow weed" , "Weed with deeply incised leaves" , "Wild plant with "clock"" .)