About to perform at American plant (6)
I believe the answer is:
cactus
'plant' is the definition.
(cactus is a kind of plant)
'about to perform at american' is the wordplay.
'about' becomes 'c' (abbreviation for 'circa').
'to perform' becomes 'act' (acting is a kind of performing).
'at' is a charade indicator (letters next to each other).
'american' becomes 'us' (abbreviation for United States).
'c'+'act'+'us'='CACTUS'
(Other definitions for cactus that I've seen before include "Prickly desert plant" , "Spiky desert plant" , "plant, succulent one" , "Spiny desert plant" , "Spiney plant of dry areas" .)