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Abstract
Long-term observations (1972–1992) at mainly weekly intervals on the phytoplankton of the eutrophic, summer stratified kettle-hole lake Plußsee, northern Germany have revealed Stephanodiscus alpinus Hustedt as an important component of the spring diatom bloom. It showed marked interannual differences in abundance, with the capacity to produce dense crops in the absence of other diatoms, contributing up to 5% of the annual phytoplankton biomass. S. alpinus has been present throughout postglacial time in Plußsee (Hickel, unpubl.). A detailed investigation on the morphology of S. alpinus is made on material from plankton samples. The development of the morphological features of S. alpinus from hemispherical cell stage to the distinctive morphology of the vegetative cell is described. It is shown that S. alpinus has several constant features and is distinct and clearly delimited from other Stephanodiscus taxa.
