Underground stem of plants such as ginger (7)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
rhizome
(Other definitions for rhizome that I've seen before include "that supplies stock" , "part of plant" , "Subterranean plant stem" , "Type of rootstock" , "Underground plant stem producing roots and shoots - zero him (anag)" .)