The life history of Polysiphonia ferulacea Suhr from North Carolina was found to include specialized asexual reproductive propagules, developmentally and morphologically resembling spermatangial branches but appearing on male, female, and tetrasporophytic plants and recycling the particular phase that produced them. A cross-gradient culture apparatus was used to determine the effects of light intensity and temperature on growth, sexual reproduction, and propagule formation. The ecological role of these propagules in the life history of this alga was discussed. Hybridization attempts between isolates of P. ferulacea from North Carolina and Bermuda revealed the existence of a genetic sterility barrier. Cytological investigations of the isolates demonstrated the presence of thirty bivalents (2n = 60) in the N. Carolina material and twenty-seven bivalents (2n = 54) in the Bermuda material. These results were discussed in the light of the presumed existence of genotypic sex determination in red algae.