Bigger volume found on plant (6)

I believe the answer is:

vaster

'bigger' is the definition.
('vast' can be similar in meaning to 'big')

'volume found on plant' is the wordplay.
'volume' becomes 'v' (abbreviation for volume in book titles).
'found on' is a charade indicator (letters next to each other).
'plant' becomes 'aster' (aster is a kind of plant).
'v'+'aster'='VASTER'

(Another definition for vaster that I've seen is " Larger".)

I've seen this clue in The Telegraph.

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