This acorn is nearly as large as a man’s fist and very heavy for its size. You can use an action to slam it into the ground and the moment you do so it sprouts and begins putting out roots. At the beginning of your next turn the acorn suddenly grows into a 30-foot tall tree appropriate to the area. When this tree appears all creatures within 15 feet must make a DC 15 Dexterity saving throw as the trunk and branches rapidly expand, taking 3d10 bludgeoning and 3d10 piercing damage on a failed save, or half as much damage on a successful one.
After this tree finishes it’s rapid growth it is just like any other tree, and will continue to grow at a normal pace.