Enchanted creature doesn't untap during its controller's untap step. Every living thing has roots in nature. Sometimes nature gets its roots into you.
Illus. Thomas M. Baxa
10/1/2009: Entangling Vines can enchant only a creature that's tapped. If at any time the enchanted creature is untapped, Entangling Vines is put into its owner's graveyard as a state-based action.
10/1/2009: If Entangling Vines is cast as a spell, it can target only a tapped creature. If the creature has become untapped by the time Entangling Vines would resolve, it's countered and put into its owner's graveyard from the stack.