Almost notice identical plant (6)
I believe the answer is:
sesame
'plant' is the definition.
(sesame is a kind of plant)
'almost notice identical' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'notice' becomes 'see' (I've seen this before).
'identical' becomes 'same' ('same' can be similar in meaning to 'identical'**).
'see' with its final letter removed is 'se'.
'se'+'same'='SESAME'
(Other definitions for sesame that I've seen before include "Open ...., says the magician" , "Open .... is a pantomime cry" , "Plant with edible seeds" , "'Open . . . . . .'' is a magic phrase to gain access" , "said to be effective in opening spell" .)