Part of plant greeting Zulu in European capital (7)
I believe the answer is:
rhizome
'part of plant' is the definition.
(I've seen this before)
'greeting zulu in european capital' is the wordplay.
'greeting' becomes 'hi' (hi is a kind of greeting).
'zulu' becomes 'Z' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' indicates putting letters inside.
'european capital' becomes 'Rome' (capital of Italy).
'hi'+'z'='hiz'
'hiz' placed into 'rome' is 'RHIZOME'.
(Other definitions for rhizome that I've seen before include "Type of rootstock" , "Underground plant stem producing roots and shoots - zero him (anag)" , "that supplies stock" , "Root" , "Underground rootstock of a plan" .)