Polysiphonia is a member of Rhodophyceae (red algae) . Red algae reproduce sexually by non-motile gametes and asexually by non-motile spores; flagella are essentially absent in this group . The other matches are correct: Brown algae produce pear-shaped biflagellate zoospores ; Marchantia (a liverwort) possesses gemma cups for asexual reproduction ; and Chlorella is explicitly described as a unicellular alga .