Willow often seen in elementary receptacles initially (5)
I believe the answer is:
osier
'willow' is the definition.
(osier is a kind of willow)
'often seen in elementary receptacles initially' is the wordplay.
'initially' suggests taking the first letters.
The first letters of 'often seen in elementary receptacles' is 'OSIER'.
(Other definitions for osier that I've seen before include "Salix" , "... source of twigs to make baskets" , "Basket-making material" , "Tree - Rosie (anag)" , "Basketry willow" .)