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A Ripple in Time quest, possible bug
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No, it said evolve an evolved grass type. So you don't fulfill it by evolving Seedot, because it isn't an EVOLVED grass type.
My suggestion would be to evolve a Skiploom (which is an evolved Hophip) into a Jumpluff. That will do the trick, as will any other EVOLVED grass form when you evolve it.
You can't use Exeggucute, because it's EVOLVED form doesn't evolve again.