First report of Navicula jakovljevicii Hustedt (Bacillariophyta) from Hungary: distribution, comparative morphology and a related species

In Hungary Navicula jakovljevicii was fi rstly recorded in biofi lm of Elodea nuttallii in 2005 in an oxbow of the catchment area of the River Danube. Subsequently, in 2006, N. jakovljevicii was also found in the same oxbow on reed stems as well. In the following years it appeared in another oxbow, suggesting an expanding distribution in the tributaries of the Danube in Hungary. The Hungarian population can be characterised as having mixed morphological features in comparison with other known N. jakovljevicii populations of Europe. When the morphological study was expanded, a similar, but 'giant form' was detect ed in fossil material. We found similarities and a possible connection between N. jakovljevicii and Navicula lucida, a diatom taxon described from a Neogene deposit in the Carpathian Basin. Despite the morphological similarities in the shape, apices, striae pattern and raphe structure of these two species, there are signifi cant differences in valve dimensions: the valves of N. lucida are larger and more heavily silicifi ed than N. jakovljevicii.