99 Potamogeton vaginatus Turcz.

This widespread species is, in Fennoscandia, limited to brackish sea water, for the rest mostly occuring in special inland waters. It belongs to the discontinuous circumpolar plants (Hultén, Circumpol. I, p. 32 and map 25). However, the distribution is incompletely known. The hybrid with P. pectinatus L. is reported from a few N. European localities.