Polysiphonia fibrillosa (Dillw.) Spreng. and P. violacea (Roth) Spreng. were shown to have a “Polysiphonia‐type” of life history in culture. They retained their morphological characteristics when grown for three generations under identical conditions and were shown to be separated by a sterility barrier. It is concluded that merging of the two taxa into one species is unwarranted. P. fibrillosa was cultured at various light intensities and temperatures and the growth compared. The production of specialized propagules, as well as other means of asexual reproduction, is reported for P. fibrillosa.