1992, Rudolf M[athias] Schuster, The Hepaticae and Anthocerotae of North America: East of the Hundredth Meridian, volume V, New York, N.Y.: Columbia University Press, pages 3-4
2009, Xin Wang, 3: New Fossils and New Hope for the Origin of Angiosperms, Pierre Pontarotti, Evolutionary Biology: Concept, Modeling, and Application, page 55