In mosses protonema is filamentous leafy green coloured structure formed as a result of the germination of the haploid spores. The protonema represents the first stage of the gametophytic generation. From the protonema there arise the leafy shoots which are known as the gametophores.
Prothallus is a flat green heart shaped structure formed as a result of the germination of the spores. It is the gametophytic phase in the life cycle of the ferns. The prothallus does not possess actual stem, leaves or roots instead it has the rhizoids. The prothallus bears the male and female sex organs. They fuse to form the zygote which then develops into a sporophytic plant body.