THE BIOLOGY OF BUTOMUS-UMBELLATUS IN SHALLOW WATERS WITH FLUCTUATING WATER-LEVEL

Butomus umbellatus L. is a plant species typical of Littoral communiti es of river and stream shores. It can form continuous stands in shallo w reservoirs with fluctuating water level. Their expansion is promoted by: (a) intensive vegetative reproduction of plants, (b) crowded spro uting from rhizome fragments on emerged pond bottom, (c) shallow water layer in the year following summer drainage. Expansion of B. umbellat us depends on ploidy level: two cytotypes were found in the Czech and Slovak Republics, differing in their reproductive ability. Seed produc tion of triploids is strongly limited (they are self-incompatible with in clones), while diploids can be fully fertile. Nevertheless, even in diploids, the efficiency of seed reproduction under natural condition s is low. Triploids spread by intensive vegetative reproduction, which is decisive for clonal growth of populations and their regeneration a fter scraping of bottom surface. During seasonal development, maximum of aboveground biomass is produced in early summer, while underground biomass increases till autumn. Growth of the plants is limited by cutt ing before maximum underground biomass is attained, or by cluck grazin g.