ON STRIA PATTERNS IN FRAGILARIA AND SYNEDRA

Abstract

Further morphological study of Fragilaria and Synedra in the restricted sense of Williams & Round (1986, 1987) has revealed differences in the stria pattern which appear to be of fundamental importance. All the examples of Fragilaria sensu Williams & Round have alternate striae without any variability and Synedra has opposite striae, often with a “fault” near the apices. The thin needle-like, usually planktonic, species placed in Synedra tend to have predominantly opposite striae but usually with some areas where the pattern fluctuates slightly. These forms require further study. Some recently described Fragilaria species are better placed in Distrionella Williams.