Essential to list each kind of shrub (3)
I believe the answer is:
tea
'shrub' is the definition.
(tea is a kind of shrub)
'essential to list each kind' is the wordplay.
'essential to' indicates a hidden word (I've seen this in other clues).
'TEA' is hidden in the letters of 'list each kind'.
'of' is the link.
(Other definitions for tea that I've seen before include "Infused beverage" , "grass" , "Drink made from leaves" , "Infusion of dried leaves" , "Oolong, for example" .)