Azolla filiculoides has been an ephemeral plant in Poland since the end of the 20th century. In the last 15 years this species appeared in 5 locations in south-west Poland. Habitat and plants of two populations became destroyed, three other still exist. A. filiculoides occurs in eutrophic or even polluted water where it forms dense mats, up to 10 cm thick. It stays sterile and propagates only in a vegetative manner. Frost resistance of Lower Silesia populations is higher than reported so far; fern may winter and rebuild the population after frost reaching 22oC. Size of the populations is changeable during the vegetation season. A. filiculoides occurs in water habitats and plant communities in which it substitutes Lemna minor
A hybrid Leuciscus leuciscus × Alburnus alburnus was found during the ichthyofaunistic studies in the Bystrzyca River, a left-bank tributary of the Odra River (SW Poland). The hybrid was identified on the basis of its intermediate features and characteristics of the parent species (biometrical, osteological and anatomical) such as opercular and dental bones, pharyngeal bones and teeth, shape of scales, number, form and structure of radial canals of the scales, and air bladder and a complex of meristic and morphometric characters. With respect to its characteristics, the hybrid is closer to dace than to bleak. The small abundance of the hybrid shows that the hybridisation was rather accidental. Key words.-Cyprinids, dace, bleak, intergeneric hybrid, morphology and osteology, biometrical analysis. a separate genus Squalius): L. leuciscus × L. idus; L. idus × L. (S.) cephalus and L. idus × Scardinius erythrophthalmus. Besides, the genus often hybridises with members of Alburnus and its close relative Chalcoalburnus -L. (S.) cephalus × A. alburnus; L. (S.) cephalus cabeda × A. albidus; L. (S.) cephalus macedonicus × Chalcoalburnus chalcoides macedonicus; L. leuciscus × A. alburnus).
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