Plant information about former staff (9)
I believe the answer is:
goldenrod
'plant' is the definition.
(goldenrod is a kind of plant)
'information about former staff' is the wordplay.
'information' becomes 'gen' (gen can informally mean information).
'about' means one lot of letters goes inside another.
'former' becomes 'old' (both can mean previous).
'staff' becomes 'rod' (both can mean a stick or cane).
'gen' going around 'old' is 'golden'.
'golden'+'rod'='GOLDENROD'
(Other definitions for goldenrod that I've seen before include "Tall-spiked plant" , "bloomer" , "Autumnal flower" , "Autumnal plant" , "Yellow-spiked garden flower" .)