Aqueous extraction of cystocarpic, tetrasporic, and vegetative individuals of Mazzaella laminariodes collected in the Magellan Ecoregion, Southern Chile, afforded sulfated galactans. Analysis by Fourier transform infrared spectroscopy (FT-IR) and by H-1 and C-13 NMR spectroscopy indicated that purified extracts from cystocarpic (CP) and vegetative individuals (VP) were mixtures of kappa/iota-type carrageenans and their precursors mu- and nu-carrageenans, whereas the aqueous extract from tetrasporic individuals was a lambda-type carrageenan. Alkaline treatment of CP and VP polysaccharides produced modified polysaccharides with lower content of sulfate groups and with a concomitant increase of 3,6-anhydrogalactose content; analysis by 2D H-1 and C-13 NMR indicated the presence of hybrid kappa-iota-carrageenans. Copolymerization of alkali-treated CP carrageenan with acrylamide was achieved by using ceric ammonium nitrate as the initiator; studies by NMR spectroscopy indicated grafting of polyacrylamide at position C-6 of beta-galactopyranosyl residues. Reaction of modified CP with acrylamide assisted by microwave irradiation in the presence of ammonium persulfate afforded a copolymer grafted at position C-2 of beta-galactopyranosyl residues.