Bijzondere sieralgvondsten in ‘De Wieden’

The Holocene quaking fens in the nature reserve ‘De Wieden’ (near Zwartsluis, in the Province of Overijssel) belong to the richest desmid sites in the Netherlands. Recently some rare species were encountered which up to then were only known from Pleistocene moorland pools in the beginning of the last century, i.e., Micrasterias apiculata, M. pinnatifida and Cosmarium striolatum. In addition to that, zygospores were found of Actinotaenium spinospermum and A. phymatosporum, two closely related species that can only be distinguished with certainty in conjugating condition. Last-mentioned species was not recorded from the Netherlands before.