Gardens conveyed in painting — Appian's first (8)
I believe the answer is:
arboreta
'gardens' is the definition.
(I've seen this before)
'conveyed in painting appian's first' is the wordplay.
'conveyed' becomes 'bore' (to bear is to transport or convey).
'in' is an insertion indicator.
'painting' becomes 'art' (painting is an art).
'appian's first' becomes 'a' (1st letter of 'appian').
'bore' going within 'art' is 'arboret'.
'arboret'+'a'='ARBORETA'
(Other definitions for arboreta that I've seen before include "shady gardens?" , "Lots of trees" , "Rare boat (anag) - botanical tree gardens" , "wooden displays" , "growth areas" .)