Neue und wenig bekannte Gomphonema-Arten (Bacillariophyceae) mit Areolen in Doppelreihen
Species of the genus Gomphonema with double rows of areolae are considered to be exceptions in the genus or the taxa bearing them have been assigned to Gomphoneis. In reality the arrangement of areolae in double rows is more common than has been suggested and can be found in all groups of the genus Gomphonema, even in taxa closely related to the typus generis. In addition, rows of partly biseriate areolae have proven to be constant characters in many species (Reichardt 2001). This paper presents descriptions and discussions of 12 new species, three of them fossil, and additional data and micrographs of three other insufficiently known Gomphonema species with biseriate areolae. These species support the statement of e.g.Hustedt (1942) that biseriate areolae on their own are not sufficient to separate corresponding taxa on generic level. Some of the new species belong to clusters of similar ,,forms" and have been seriously confused up to the present. By an exact classification of these species the definition of the corresponding groups of taxa becomes more precise.