Recent approaches to the taxonomy of the Gracilariaceae (Gracilariales, Rhodophyta) and the Gracilaria verrucosa problem

Recognition of species in the Gracilariaceae, often notoriously difficult, is being aided by a combination of classical and modern techniques. We review some recent findings and present new results that may lead to redefinition of Gracilaria verrucosa, the type species of its genus. Plastid DNA restriction profiles (patterns of banding obtained by electrophoresis of DNA after restriction endonuclease digestion) from eleven strains ascribed to G. verrucosa indicated that the concept of this species in northern Europe includes possibly three taxa, one of which is known now to be a species of Gracilariopsis. In contrast, restriction profiles from Argentinian and Japanese strains were closely similar to the predominant pattern for European G. verrucosa. Profiles of several other strains, from the western Atlantic and eastern Pacific, were dissimilar to the European group and to each other. A chromosome number of n = 24 was determined for a representative of the predominant European group, and preliminary results of hybridization trials suggest that these strains, and others with approximately the same plastid DNA restriction pattern, are interfertile.