A revision of the diversity and distribution of Potamogeton hybrids in the Czech Republic is presented. Thorough examination of herbarium material and recent extensive field studies revealed the present and/or past occurrence of eight Potamogeton hybrids in the Czech Republic. In addition tomorphological characters, stem anatomy and/or molecular analysis were used to identify some of the hybrids. All the hybrids detected are between broad-leaved species of the genus, suggesting that hybrids between linear-leaved species may be overlooked because of the overall morphological similarity of taxa within this group. Four of the hybrids identified, P. ×nitens, P. ×olivaceus, P. ×sparganiifolius and P. ×undulatus, are recorded for the first time from the Czech Republic. Four of the hybrids are now extinct in the Czech Republic and the extant hybrids are rare. The occurrence of P. ×lintonii was not confirmed; the previous record was based on extreme forms of P. gramineus. The name P. ×concinnitus, proposed for a putative hybrid combination “P. pusillus × P. crispus”, was lectotypified and reduced to a synonym of P. crispus. Although the absolute number of finds of specimens of Potamogeton hybrids per decade is increasing, this is not a result of more frequent hybridization but of an increase in recording activity. Most records for recent decades are associated with targeted research by a few experts. The typical habitat of Potamogeton hybrids in the Czech Republic are ponds that were previously drained in summer and allowed to dry out. Many historical localities disappeared when the traditional fishpond management was largely abandoned and fish farming become more intensive. In the 19th century in particular some hybrids were recorded also in rivers but these occurrences generally disappeared after the extensive channelling of rivers at the beginning of the 20th century. Many hybrids occur at the same localities as their parents but it is documented that hybrids can persist vegetatively in the absence of the parental species, presumably as relics of the previous presence of the parent plants. Although almost all Potamogeton hybrids are consistently sterile, a cultivation experiment showed that P. ×angustifolius set seeds that were fertile and successfully produced adult plants.
The occurrence in the Mediterranean part of Europe of the African species Potamogeton schweinfurthii is recorded for the first time. So far, this native but overlooked species has been found on five major Mediterranean islands: Corsica, Sardinia, Malta, Kefallinía (Ionian Islands, Greece) and Crete. The species is most similar and presumably closely related to the mainly Eurasian P. lucens, with which it has been partly confused. The nomenclature and a description of P. schweinfurthii are provided, and its taxonomy and how it differs from similar taxa discussed. All known localities are listed, together with voucher specimens preserved in the major European herbaria. A distribution map of P. schweinfurthii in the Mediterranean region is presented.
Specimens of Viola elatior (VE), V. pumila (VP) and V. stagnina (VS) in 40 Austrian, Czech and Slovak public herbaria were revised, a total of almost 1750 specimens from the three countries. Apart from VE, the quality of the original identifications was rather poor, especially of VS, which was frequently confused with VP and V. canina. This, together with the confusion of nomenclature that persisted during the 19th century, made the old literature records unreliable. Hybrids are usually difficult to identify and are rarer than generally believed. VS and VP have similar distribution patterns: they occur mainly on floodplains of large lowland rivers and in adjacent hills in the N part of Bohemia, S and Central Moravia, E Austria and S Slovakia; they may be classified as river corridor plants. VS differs from VE and VP mainly by its presence in S Bohemia and its absence from large parts of S Slovakia, as well as its rarity in Austria and Slovakia. All three species grow predominantly in regions with a relatively warm and dry climate: most localities are situated in regions with a mean annual temperature of 7–11 °C and mean annual precipitation 401–700 mm. A temporal analysis of records revealed that all three species are declining in all three countries: generally, this decline is weakest in Austria, with 46–61% of grid cells with occurrences confirmed after 1980 (compared with the number of grid cells with records for 1801–2008), and strongest in Slovakia, with 18–32% of grid cells with occurrences confirmed after 1980. The decline is due mainly to the canalization of rivers and subsequent changes in land use, urbanization and recently afforestation. VE may also be endangered by modern forestry practices. The inclusion of all three species in national Red Lists and subsequent conservation measures are justified and necessary, though national Red List status may differ between countries.