The life cycle of Polysiphonia shows three distinct phases. They are;
The free living gametophytic thallus bearing spermatia and carpogonia.
A parasitic carpo sporophyte formed by the germination of the zygote.
Free living tetra sporophyte formed by germination of carpospores.
Thus the life cycle of Polysiphonia is characterized by the production of one somatic gametophytic phase and two somatic sporophytic phase formed by the carpo sporophyte and tetra sporophyte. Thus the life cycle is called as diplodiplohaplontic lifecycle.