National emblem saint introduced to Leith, oddly (7)
I believe the answer is:
thistle
'national emblem' is the definition.
(I've seen this before)
'saint introduced to leith oddly' is the wordplay.
'saint' becomes 'st'.
'introduced to' means one lot of letters goes inside another.
'oddly' is an anagram indicator.
'leith' with letters rearranged gives 'thile'.
'st' going within 'thile' is 'THISTLE'.
(Other definitions for thistle that I've seen before include "Lithest (anag) - plant" , "Scotland's emblem" , "Scottish plant emblem" , "Scottish flower" , "Prickly plant (Carduus)" .)