Three types of plants are seen in Polysiphonia. They are:
The free living haploid plant body which are concerned with the sexual reproduction and production of gametes which is called as gametophyte. There are two kinds of gametophyte they are the male gametophyte and the female gametophyte.
Zygote develops to a diploid plant body which remains on the female gametophyte. Which then produces diploid carpospores and it is called the carpo sporophyte.
The carpospores on germination give rise to a free living and independent diploid plant. It is morphologically similar to the gametophyte plant. It produces the haploid tetra spores and it is called as the tetra sporophyte.
The sexual reproduction in the Polysiphonia is oogamous which occurs in gametophyte and it is dioecious. The male sex organ is the spermatagia and the female sex organ is the carpogonia. The apices of the male plant bear the male trichoblast which is short and 2 celled. The 2 celled stalk is forked into spermatangial branch and sterile trichoblast. The spermatia are uninucleated protoplasm; it is transported to female sex organs. The female gametophyte develops on the female trichoblast. The carpogonia is a flask shaped structure which has a basal swollen portion and a terminal long slender neck. During the fertilization the mature non-motile spermatia is transported by the water current. And it finally reaches the basal swollen portion of the carpogonium; the fusion occurs and the diploid nucleus that is the zygote is formed. The zygote develops to a diploid plant body which remains attached to the female gametophyte. This plant body produces the carposporophyte which produces the carpospores. The enveloping threads which encloses the carpo sporophyte forms the Cystocarp. The Cystocarp is an oval urn shaped structure attached laterally to the main axis which has an opening known as the ostiole. Pericarp is wall two layered wall of the Cystocarp. Each Cystocarp encloses many carpo sporangia which produces the carpospores. The carpospores are liberated through the ostiole and it then germinate when falls on suitable substratum. After germination it develops to Polysiphonous thallus which is free living independent diploid tetra sporophyte. It is similar to the gametophytic plant body. The plant body produces the tetra sporangia which produces the tetra spores. These tetra spores on germination give rise to the gametophytic thallus.