Plant from east — a chap will be tedious about that (9)
I believe the answer is:
hellebore
'plant' is the definition.
The answer is an example.
'east a chap will be tedious about that' is the wordplay.
'east' becomes 'e' (abbreviation).
'a chap will' becomes 'hell' (contraction of 'he will').
'be tedious' becomes 'bore' (I can't explain this - if you can you should give a lot more credence to this answer).
'about that' is an insertion indicator.
'hell'+'bore'='hellbore'
'e' put inside 'hellbore' is 'HELLEBORE'.
'from' is the link.
Can you help me to learn more?
(Other definitions for hellebore that I've seen before include "aconite?" , "In bed I grow" , "it comes out at Christmas" , "Poisonous plant" , "Flower of the lily family found in rebel hole" .)