Climber's cleat is abandoned around mountain top (8)
I believe the answer is:
clematis
'climber's' is the definition.
(type of climbing plant)
'cleat is abandoned around mountain top' is the wordplay.
'abandoned around' is an insertion indicator.
'top' says to take the initial letters.
The initial letter of 'mountain' is 'm'.
'cleat'+'is'='cleatis'
'cleatis' going around 'm' is 'CLEMATIS'.
(Other definitions for clematis that I've seen before include "Ornamental climber" , "Popular climbing plant" , "Climbing garden plant" , "flower" , "bloomer" .)