Approaches to the identification of terete Brazilian Gracilariaceae (Gracilariales, Rhodophyta)

Most of the agar production in the world now comes from terete species of Gracilariaceae, a notoriously difficult group with regard to species circumscription. We have studied different populations of such algae from Brazil and from abroad in order to ascertain their identity and relationship. We based our taxonomic concepts on traditional morphological markers and attempted crosses between putatively interspecific and geographically isolated intraspecific populations. Data from the crosses helped in the recognition of genera and species with convergent morphologies and between disjunct populations. Our results show that configuration of male reproductive structures and some features of cystocarp anatomy are reliable taxonomic characters whereas some morphological features, such as gross thallus morphology and branching pattern, are not.