Prothallium

Prothallium, otherwise written Prothallus, is the gametophyte of the Pteridophyta (q.v.), i.e. that plant, generation, or stage in the life-cycle, that bears the sexual reproductive organs. It is a small thalloid body, often a mere plate of cells one cell thick, leading a short but independent life and without any trace of vascular tissue. It may, or may not, contain chlorophyll. In heterosporous forms the prothallia are reduced to mere minute appendages of the spores, and in homosporous groups they may be dioecious, bearing only antheridia or only archegonia.