Plant in which waiter is maltreated (8)
I believe the answer is:
wisteria
'plant' is the definition.
(wisteria is a kind of plant)
'waiter is maltreated' is the wordplay.
'maltreated' is an anagram indicator.
'waiter'+'is'='waiteris'
'waiteris' anagrammed gives 'WISTERIA'.
'in which' acts as a link.
(Other definitions for wisteria that I've seen before include "I saw tire in this vine with the long flower clusters" , "Climbing lilac-flowered shrub" , "A flower, I swear it" , "Large climbing shrub, often attached to house" , "Climber" .)