Plant of marsh and lake around northeast (6)
I believe the answer is:
fennel
'plant' is the definition.
(fennel is a kind of plant)
'marsh and lake around northeast' is the wordplay.
'marsh' becomes 'fen' (synonyms).
'and' is a charade indicator (letters next to each other).
'lake' becomes 'L' (geographical abbreviation).
'around' is an insertion indicator.
'northeast' becomes 'NE' (abbreviation).
'fen'+'l'='fenl'
'fenl' enclosing 'ne' is 'FENNEL'.
'of' acts as a link.
(Other definitions for fennel that I've seen before include "Aromatic yellow plant of the parsley family" , "Plant used for seasoning" , "Culinary plant" , "type of seasoning" , "Herb Len raised behind the fen" .)