Three Caribbean species of Callithamnion are recognized to be species of Aglaothamnion. The life history of Aglaothamnion herveyi (Howe) comb. nov., completed in culture, was a Polysiphonia type, but this species also reproduced by propagules in both gametophytic and tetrasporophytic plants. Propagules recycled their respective phases. Aglaothamnion herveyi is typically covered with fine sediment, making the plant very inconspicuous in the field. The morphology and taxonomic status of Aglaothamnion felipponei (Howe) comb. nov. is clarified, and Aglaothamnion uruguayense (W. Taylor) comb. nov. is proposed.