To remove the petals from a flower.
From de- (remove) + petalize (from petal, which comes from Latin petalum meaning 'leaf'). A botanical or horticultural term that is quite rare.
In Victorian times, when people played 'loves me, loves me not' by pulling flower petals, they were literally depetaling flowers—it's probably one of the few times this technical word actually describes something most people do.
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