Nypa pollen diversity in middle Eocene mangroves at the edge of the southern Proto-North Sea (Helmstedt, northern Germany) – a statistical approach

A variety of Spinizonocolpites pollen types which were commonly related to the mangrove palm Nypa has been recorded in marine beds intercalated in the lignite-bearing middle Eocene Helmstedt Formation in northern Germany. They are further confirmation for the existence of a tropical mangrove at the southern coast of the Proto-North Sea. Seven morphological parameters related to pollen size, exine thickness and ornamentation have been measured for 182 Spinizonocolpites grains by light microscopy (LM) and scanning electron microscopy (SEM) to reveal the morpho-diversity within the assemblage of Nypa pollen. The use of different univariate and multivariate statistical analyses such as cluster analysis and principal component analysis (PCA) objectively allow differentiation of five significantly different morphotypes, which may be assigned to four previously described Spinizonocolpites species and a new morphotype. However, S. prominatus and the new morphotype form a continuum in the PCA with S. echinatus and S. baculatus as endmembers. Only S. cf. quilonensis lies outside the common range of morphological variation of the other species of Spinizonocolpites. Therefore, the existence of only two different Nypa species in the mangrove at Helmstedt is indicated despite the occurrence of five pollen morphotypes. Our study therefore illustrates that morpho-diversity of pollen is not necessarily related to species diversity in the parent plants.