Medicinal shrub (6)
I believe the answer is:
cassia
'medicinal shrub' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cassia that I've seen before include "Source of senna" , "Tree providing senna" , "Coarse bark" , "Tree producing senna" , "Medicinal shrub with an aromatic bark" .)