Staunch good man having me back (4)
I believe the answer is:
'staunch' is the definition.
(I've seen this before)
'good man having me back' is the wordplay.
'good man' becomes 'st'.
'having' means one lot of letters go next to another.
'back' says the letters should be written in reverse.
'me' back-to-front is 'em'.
(Other definitions for stem that I've seen before include "Check - part of a plant" , "Upward part of a plant" , "supporter of flag, for example" , "Vertical part of flower or drinking glass" , "Flower's stick" .)