The fourth part of a revision of linear-leaved species of the genus Potamogeton in the Czech Republic is given, dealing with P. pusillus s.l. and P. trichoides. The appropriate taxonomic concept and species delimitation within P. pusillus s.l. are discussed. Because of still unresolved taxonomic difficulties and high percentage of specimens that cannot be assigned to one of the two traditionally distinguished species, P. pusillus s. str. (syn. P. panormitanus) and P. berchtoldii, the broader concept of P. pusillus s.l. has tentatively been adopted in this revision. This species complex is widespread in the Czech Republic, absent only in relatively small areas of the highest elevations and the driest areas without suitable biotopes. P. pusillus s.l. is the commonest taxon of Potamogeton in standing waters. P. trichoides, a well defined species distinguished by several morphological characters, occurs scattered mainly in S, C and E Bohemia and S and C Moravia, with most localities concentrated in S Bohemia. It is considered as strongly threatened species of the Czech flora. Species descriptions, relevant synonyms, illustrations, a list of specimens examined and distribution maps are provided for both species. P. rutilus was once reported from the Czech Republic in error. No specimen from this country has been found in herbaria.
The last part of a revision of linear-leaved species of the genus Potamogeton in the Czech Republic focuses on P. pectinatus. This species is the only member of subgenus Coleogeton occurring in this country. Species description, relevant synonyms, illustrations, a list of specimens examined and a distribution map are provided. P. pectinatus is widespread in the Czech Republic; it is the most common Potamogeton species particularly in runningwaters. P. pectinatus still quite often grows in most lowland rivers and their basins.
The third part of a revision of linear-leaved species of the genus Potamogeton in the Czech Republic is given. Two species, P. obtusifolius and P. friesii, are dealt with in this contribution. Species descriptions, relevant synonyms, illustrations, a list of specimens examined and distribution maps are provided. P. obtusifolius grows almost exclusively in the Bohemian part, particularly in S and E Bohemia, whereas in Moravia it is confined to a few localities mainly in its NE part (Silesia). It is classified as a threatened species of the Czech flora. P. friesii has been collected only in a few localities in C and NE Bohemia. Last time it was seen in 1989 but has not been confirmed in the site since then; thus the species belongs among missing (and probably extinct) taxa in the Czech Republic.