Grass-like plant in small border (5)
I believe the answer is:
sedge
'grass-like plant' is the definition.
(I've seen this before)
'small border' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'border' becomes 'edge' ('edge' can be a synonym of 'border').
's'+'edge'='SEDGE'
'in' is the link.
(Other definitions for sedge that I've seen before include "Herons" , "Marsh grass" , "plant with triangular stems" , "Grass-like plant growing in wet places" , "Grass-like plant growing in marshes" .)