Zygote transfer and post-fertilization stages in Mesophyllum (Mesophyllaceae, Corallinales, Rhodophyta)

Zygote transfer in Mesophyllum lichenoides involves a cell tube developed from the basal part of the carpogonium, connecting it with the supporting (auxiliary) cell of the same branch system (procarpy). After zygote transfer, neighbouring supporting and hypogenous cells coalesce to form a fusion cell, where subtending basal cells are also connected. In Mesophyllum philippii, the fusion cell includes at least one carpogonium and proliferates radially to produce gonimoblast filaments, which cut off terminal carposporangia. The cytoplasm of hypogenous cells, which do not participate in the fusion cell, is sucked in the gonimoblast filaments, leaving characteristic cell wall remains (linking carpogonia to gonimoblast filaments). In both species, the subtending basal cells establish wide connections to the fusion cell, and cells of the gonimoblast filaments, but remain intact and do not coalesce.