@Elliandre, whether you can evolve a plant in a park (or in the open world for that matter) depends on how the plant was placed. If it's a "wild" variety, then no you cannot, but if it's a planted/grown variety, then yes you can. For example, though you can't evolve most plants in the open world, you can evolve the ones planted in the public space gardening area of the Old New Henford neighborhood in HoB.