Life history of Gymnogongrus griffithsiae (Phyllophoraceeae, Gigartinales) from Ireland: implications for life history interpretation in the Rhodophyta

Tetraspores of the marine red alga Gymnogongrus griffithsiae (Turner) Martins (Phyllophoraceae, Gigartinales), the type species of the genus Gymnogongrus, gave rise in culture to erect, multiaxial, dichotomously divided thalli that developed into monoecious gametophytes. Procarps consisted of a large supporting cell and a three-celled carpogonial branch provided with a one- or two-celled sterile branchlet. Fertilized carpogonia fused with auxiliary cells, and initials of inwardly growing filaments were cut off from the auxiliary cells. Outwardly growing filaments subsequently developed from some parts of the inwardly growing filaments and directly from the auxiliary cells. They penetrated into the cortex of the erect axes and gave rise to pustule-like tetrasporoblasts, which in due course produced intercalary, seriate tetrasporangia in distinct sori. Released tetraspores developed into plants similar to those of the first generation. The relative fluorescent intensity of nuclear DNA stained with DAPI indicated that outer cortical cells of upright gametophytes, released spermatia, and tetraspores were haploid, whereas distal perithallial cells of tetrasporophytes and undivided tetrasporocytes were diploid. This confirms previous reports that meiosis occurs in the tetrasporangium during the formation of tetraspores. This type of life history is found only in some members of the Phyllophoraccae and a species of Pikea of the Dumontiaceae and is best referred to as the Gymnogongrus griffithsiae-type life history. The life history is considered to have arisen via multiple evolutionary events.