Number four, ie top shrubs and climbers (5)
I believe the answer is:
ivies
'climbers' is the definition.
(ivies are climbing plants)
'number four ie top shrubs' is the wordplay.
'number four' becomes 'iv' (Roman numerals for four. I am not sure about the 'number' bit.).
'top' says to take the initial letters (in a down clue, the first letter is top).
The first letter of 'shrubs' is 's'.
'iv'+'ie'+'s'='IVIES'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for ivies that I've seen before include "Vines with evergreen leaves" , "Climbers" , "Climbing plants with evergreen leaves" .)