A hypothesis of phylogenetic relationships inferred by parsimony analysis of plastid-encoded rbcL sequences is presented for red algae containing agar-and carrageenan-like phycocolloids ; rbcL encodes the large subunit of ribulose 1,5 bisphosphate carboxylase/oxygenase . Previous studies have shown that Floridean families that contain sulfated galactans as cell wall components are resolved as a monophyletic Glade sister to the agarophyte order Ahnfeltiales . Families that have been identified as containing kappa-type carrageenans, often in addition to lambda-type carrageenans, are resolved in three clades : (1) a complex containing the families Solieriaceae, Cystocloniaceae, Hypneaceae, Caulacanthaceae, Tichocarpaceae, Furcellariaceae, and the genera Turnerella and Opuntiella ; (2) the Gigartinaceae and Phyllophoraceae, and (3) the genus Endocladia. Except for 7ichocarpus and Endocladia, these are all members of the Gigartinales sensu Kylin (1956) . Most of the families previously placed in the Cryptonemiales by Kylin appear to contain only lambda-type carrageenans . These fall into two groups, one that clusters with typical carrageenophyte-and the other with typical agarophyte-taxa. The first of these includes the families Polyideaceae, Kallymeniaceae, Dumontiaceae, and Rhizophyllidaceae . The second includes the type family of the Cryptonemiales, the Halymeniaceae, which is divisible into two well-supported clades, one of which possesses special lambda-like carrageenans, the aeodans, and the Schizymeniaceae, a recently created family containing two former gigartinalean genera . The agarophyte orders Gelidiales, Gracilariales and Ceramiales are well resolved as monophyletic clades, but their topological positions are poorly resolved . The Gelidiales and Ceramiales are associated, but the Gracilariales is included in a Glade that contains families belonging to the Rhodymeniales, a possible agarophyte order. Finally, two groups that may contain lambda-like carrageenans, the Plocamiales and the Sarcodiaceae, are resolved as separate clades .