Bird sits on new article in plant (5)
I believe the answer is:
henna
'plant' is the definition.
(plant which henna dye is made from)
'bird sits on new article' is the wordplay.
'bird' becomes 'hen' (hen is a kind of bird).
'sits on' says to put letters next to each other.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'article' becomes 'a' (the indefinite article in English).
'hen'+'n'+'a'='HENNA'
'in' acts as a link.
(Other definitions for henna that I've seen before include "Red hair dye" , "(Shrub producing) reddish dyestuff" , "Reddish-brown plant dye" , "Reddish dye for hair etc" , "Reddish-brown hair-dye" .)