Revision of Bolboschoenus (Asch.) Palla (Cyperaceae) in the Netherlands

In the last decades, Van der Meijdenʼs editions of the Heukels’ Flora recognized only a single taxon in the 'Bolboschoenus maritimus group’ for the Netherlands: Bolboschoenus maritimus (L.) Palla, formerly known as Scirpus maritimus L. This is probably because the previously recognized infraspecific taxa were solely based on inflorescence architecture. These characters, however, vary between and within populations, and even within clones or individuals. However, in Central Europe the study of a new character, pericarp morphology, resulted in new insights in the taxonomy of the ‘Bolboschoenus maritimus group’. A species new to science, B. laticarpus Marhold, Hroudová, Ducháček & Zákr., has been reported to occur in the Netherlands as well. In this study, we aimed at unravelling the occurrence, the distribution and the ecology of this new species. We studied herbarium collections, in situ populations and database records in order to make a revision of Bolboschoenus (Asch.) Palla in the Netherlands. We addressed possible ecological explanations for the distribution of the species found in this study by measuring dispersal traits of achenes as a proxy for differences in dispersion ecology. We found that Bolboschoenus laticarpus is common and widespread in the Netherlands, and that it is the dominant species of the genus in inland freshwater fluviatile systems. All other specimens belonged to B. maritimus, which still showed considerable morphological variation. However, we do not wish to re-establish formerly used taxonomic ranks at the infraspecific level to classify this variation. Achene traits indicated that both species are readily dispersed by hydrochory and endozoochory, but this cannot not explain the differences in distribution in the Netherlands. We provide a key for the genus Bolboschoenus in the Netherlands and present a distribution maps, illustrations and photos of both species. We discuss the phytosociological implications of our research based on literature and vegetation relevés with B. laticarpus. All revised herbarium specimens are listed in an appendix.