A Potamogeton hybrid found growing in the absence of parental species in a South Bohemian stream, Czech Republic, was subjected to molecular analyses to identify its exact identity. RFLP of the ITS region confirmed its previous morphological identification as P. natans × P. nodosus (= P. ×schreberi). A comparison of its RFLP pattern with those of P. gramineus, P. lucens and P. polygonifolius unambiguously excluded the possibility that the investigated plants are specimens of other similar hybrids (P. ×fluitans, P. ×sparganiifolius, P. ×gessnacensis). The discovery of P. ×schreberi in South Bohemia is the first record of this hybrid for the Czech Republic. So far, it is known only from five countries and the Czech clone is one of a few extant clones of this hybrid in Central Europe. Chloroplast DNA sequencing identified P. nodosus as the maternal parent although at present this species neither occurs at the locality, nor upstream, nor in the entire drainage basin. The other species, P. natans, only occurs downstream of the locality in isolated side pools in a former stream bed and fishponds in an adjacent drainage basin. The available data indicate that this hybrid has persisted vegetatively at this locality for some time in the absence of its parents.
Traditionally, only two native localities of Ligularia sibirica have been reported from the Czech Republic. In the present paper, a correction is made as to the founder of the locality between Jestřebí and Staré Splavy near Doksy (50°36'23" N, 14°36'54" E) which was discovered by J. Ch. Neumann in 1814 the latest, i.e. earlier than thought. The species has been retreating from this locality because of changes in environmental conditions, with the decrease of groundwater level after amelioration in 1928 being the most important factor. However, the species is not yet endangered in the locality. The second locality is between Bělá pod Bezdězem and Bakov nad Jizerou (50°29'45" N, 14°54'39" E) and it was not discovered by anybody of those reported up to now but by V. J. Sekera; the discovery was not made in 1854 but as early as in 1843. This locality consists of several populations and its size has increased during the last 100 years. Bohemian localities, which are rather distant from the continuous distribution of the species, originated in the early postglacial period (Praeboreal) and represent remnants of former more extensive distribution in this region. The cultivation of the species and its secondary occurrence are rare and mostly unimportant events.