I think this got in the wrong box at some point. I am very sure this is our very own Michigan State Stone: the 'Petosky Stone'; Scientific genus Hexagonaria percarinata. They are from the Devonian period of earth's history. Hexagonaria percarinata only lived between ~Traverse City and Petosky, in an ancient shallow sea that once covered our region. John Vanregenmorter, 11/1/2018
Also, it is Cnideria (Jellyfish and corals). More specifically it is a colonial Rugose coral. It is not a plant. John Vanregenmorter, 11/1/2018