XVI International Botanical Congess

For an evaluation of changes in biodiversity it is essential to have earlier references as base line. With the recent change of taxonomic concepts in the diatoms, species lists represent historical biodiversity only fragmentarily. 100 year old samples from Lake Malawi make it possible to study these records directly. From these 21 samples - epilithon, epipelon, plankton, sediment - mainly from the Tanzanian side, Otto Müller (1903-1910) recorded 211 diatom taxa of which 49 he described as new. His emphasis was on new taxa within the genera Melosira, Surirella and Rhopalodia, Gomphocymbella he described newly from this lake. Reinvestigation of these samples exceeds his findings, showing that three recently described taxa are not new to the lake. Modern diatom taxonomy is forcing us to review concepts on endemism and biogeography, and thus on the biodiversity of diatoms.