Revisiting the systematics of Ganonema (Liagoraceae, Rhodophyta) with emphasis on species from the northwest Pacific Ocean

Abstract

:The genus Ganonema was distinguished from the other genera in the Liagoraceae morphologically by several reproductive and vegetative features, including spermatangia formed in dense, dendroidal clusters; carpogonial branches remaining unfused after fertilisation, having compact gonimoblasts; and medullary filaments being relatively broad. In addition, the generitype G. farinosum was uniquely characterised by its carpogonial branches being borne on small, specialised branches arising from the basal part of assimilatory filaments, a feature not seen in other species of Ganonema. Our molecular analyses, incorporating several species currently attributed to Ganonema, showed that the genus was polyphyletic and represented in three independent lineages, one including the generitype G. farinosum, a second including ‘G’ dendroideum, and a third containing three ‘Ganonema’ (‘G.’ clavatum, ‘G.’ borowitzkae and ‘G.’ samaense) from the northwest Pacific Ocean. We have therefore proposed two segregate genera, Gloiocallis gen. nov. for ‘G.’ dendroideum and Hommersandiophycus gen. nov. for ‘G.’ clavatum, ‘G.’ borowitzkae and ‘G.’ samaense. Morphologically, Gloiocallis differed from Ganonema and Hommersandiophycus in having only a few involucral filaments produced from the cortical cells above the supporting cell and most cells of the gonimoblasts differentiating into carposporangia. Hommersandiophycus can be separated from related genera by a combination of unfused carpogonial branches, involucral filaments produced from the cortical cells above and below the supporting cell and its neighbouring cells, carposporangia differentiating sequentially in chains of two to three and gonimoblasts being hemispherical to spherical. The taxonomy of other species currently placed in Ganonema but not analysed in this study requires further work.