Trees in line with curved forms (7)
I believe the answer is:
larches
'trees in' is the definition.
'larches' can be an answer for 'trees' (I've seen this before). I am not certain of the 'in' bit.
'line with curved forms' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'with' says to put letters next to each other.
'curved' becomes 'arc' (I've seen this before).
'forms' becomes 'hes' (I can't explain this - if you can you should give a lot more credence to this answer).
'l'+'arc'+'hes'='LARCHES'
Can you help me to learn more?
(Other definitions for larches that I've seen before include "Pine trees for Charles" , "Coniferous trees" .)