Lines, we hear, stood up (4)
I believe the answer is:
rose
'stood up' is the definition.
(I've seen this in other clues)
'lines we hear' is the wordplay.
'lines' becomes 'rows' (row is a kind of line).
'we hear' indicates a 'sounds like' (homophone) clue.
'rows' sounds like 'ROSE'.
(Other definitions for rose that I've seen before include "beauty" , "reached for the skies" , "Perforated nozzle" , "Gained height" , "Went up; plant" .)