Shrub seller in America south of Los Angeles (8)
I believe the answer is:
lavender
'shrub' is the definition.
(I know that lavender is a type of shrub)
'seller in america south of los angeles' is the wordplay.
'seller in america' becomes 'vender' (US spelling of 'vendor').
'south of' says to put letters next to each other (in a down clue, some letters go under others).
'los angeles' becomes 'LA' (abbreviation).
'vender' after 'la' is 'LAVENDER'.
(Other definitions for lavender that I've seen before include "Plant with aromatic mauve flowers" , "Shrub with fragrant purple flowers, used to scent linen" , "Fragrant purple flower used to scent linen etc" , "Plant prized for its scent" , "Light bluish-purple" .)