Grass from a poster (7)
I believe the answer is:
esparto
'grass' is the definition.
(type of grass plant)
'from a poster' is the wordplay.
'from' is an anagram indicator (from the letters).
'a'+'poster'='aposter'
'aposter' is an anagram of 'ESPARTO'.
(Other definitions for esparto that I've seen before include "Coarse type of grass" , "Grass, used for ropes, paper" , "Grass used in making rope" , "Tap Eros for the grass" , "Fibrous grass" .)