Abstract: The genus Liagora is broadly defined and incorporates species with diverse carposporophyte developmental patterns, including species having compact gonimoblasts with discrete involucral filaments and species having diffuse gonimoblasts with intermingling involucral filaments and fused or unfused carpogonial branches. In order to clarify the phylogenetic significance of these patterns of cystocarp development, we inferred the species relationships of Liagora with diffuse gonimoblasts and related genera from the northwestern Pacific Ocean, based on rbcL sequence analysis. Molecular analyses demonstrated that Liagora is polyphyletic and the species currently recognized are clustered in three distinct clades. We revise the taxonomy by presenting new genera for two of these clades. The clade containing the generitype, L. viscida retains the name Liagora. The second clade, containing Liagora perennis, is described as Macrocarpus gen. nov. The third clade, for which we propose the new genus Neoizziella, contains Neoizziella asiatica sp. nov. and N. divaricata comb. nov. (basionym: Liagora divaricata C.K. Tseng). Neoizziella is characterized by morphologically similar, intermingling involucral and gonimoblast filaments, carpogonial branch cells that remain discrete, and small, undivided carposporangia. In contrast, Macrocarpus has larger, divided carposporangia, in addition to diffuse gonimoblasts with unfused carpogonial branches. The genera Akalaphycus and Stenopeltis, which also possess diffuse gonimoblasts, can be separated from these genera by a combination of cortical and carpogonial features.