Prothallium
![Prothallus of the tree fern Dicksonia antarctica (note new moss plants for scale)](/Images/godic/202502/04/Dixonia_prothallus2611.jpg")
A prothallium, or prothallus (from Latin pro = forwards and Greek θαλλος (thallos) = twig) is usually the gametophyte stage in the life of a fern or other pteridophyte. Occasionally the term is also used to describe the young gametophyte of a liverwort or peat moss as well.