Plant with numerical identification on island (9)
I believe the answer is:
digitalis
'plant' is the definition.
(digitalis is a kind of plant)
'numerical identification on island' is the wordplay.
'numerical identification' becomes 'digital' (I am not sure about this - if you are sure you should believe this answer much more).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'island' becomes 'is' (geographical abbreviation).
'digital'+'is'='DIGITALIS'
'with' acts as a link.
Can you help me to learn more?
(Other definitions for digitalis that I've seen before include "Heart drug prepared from foxglove leaves" , "medicinal drug" , "Drug from foxgloves" , "Cardiac stimulant prepared from 11" , "Drug derived from foxglove leaves" .)