Yellow-flowered tree (8)
I believe the answer is:
laburnum
'yellow-flowered tree' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for laburnum that I've seen before include "Source of poison" , "Shrub known as golden chain" , "Poisonous shrub with yellow flowers" , "Tree with yellow flowers and poisonous seeds" , "Poisonous plant" .)