Line acquires a new tree (5)
I believe the answer is:
rowan
'tree' is the definition.
(type of tree)
'line acquires a new' is the wordplay.
'line' becomes 'row' (a row or line of things).
'acquires' says to put letters next to each other.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'row'+'a'+'n'='ROWAN'
(Other definitions for rowan that I've seen before include "Mr Atkinson, actor" , "Mountain ash (at Lambeth!)" , "Tree with orange-red berry-like fruits" , "Tree bearing bright red berries" , "Atkinson or Williams" .)