More than one plant is seen covering hillside? (6)
I believe the answer is:
irises
'more than one plant' is the definition.
(iris is a flower)
'is seen covering hillside?' is the wordplay.
'seen covering' means one lot of letters goes inside another.
'hillside?' becomes 'rise' (a bit of ground which rises).
'is' placed around 'rise' is 'IRISES'.
(Other definitions for irises that I've seen before include "Flags" , "Eye membranes or showy flowers." , "Subject for van Gogh" , "Flowers painted by Van Gogh" , "Parts of eyes or flowering plants" .)