Small, ultimately stunted and unwanted plant (4)
I believe the answer is:
weed
'unwanted plant' is the definition.
(I've seen this before)
'small ultimately stunted' is the wordplay.
'small' becomes 'wee' ('wee' can be similar in meaning to 'small').
'ultimately' suggests the final letters.
The last letter of 'stunted' is 'd'.
'wee'+'d'='WEED'
'and' acts as a link.
(Other definitions for weed that I've seen before include "Useless plant - useless person" , "nuisance in bed" , "pot" , "Uncultivated plant" , "gone!" .)