Systematics of red algae (Rhodophyta)

Abstract

Red algal systematics is in a state of flux unparalleled since the early decades of this century. Ultrastructural and biochemical studies are providing features for a revised classification at ordinal and supraordinal ranks, whereas characters of vegetative and reproductive morphology continue to establish discontinuities among taxa at lower ranks. Cytological, biosystematic, and chemotaxonomic contributions are viewed as useful in defining relationships at specific and infraspecific ranks. Chemotaxonomic studies, depending on the properties of the taxa that are being studied, are applicable at all taxonomic levels. The taxonomic importance of life histories and themes of vegetative morphology, including spore germination, heterotrichy, initiation and differentiation of thalli are discussed at length. Homologies of auxiliary cells, carpogonial branches, and connecting filaments are examined in the context of relationships among Corallinales, Cryptonemiales, Gigartinales, and Rhodymeniales, and their included families. Based on a phylogenetic analysis, we provide a synopsis of our classification of Rhodophyta, together with the features that define each order.