Ecology of two cytotypes ofButomus umbellatus I. Karyology and breeding behaviour

Chromosome numbers were counted inButomus umbellatus from 99 localities in both Czech and Slovak Republics and the karyotype morphology was studied. Basic chromosome sets are asymmetrical and uniform among diploids (2n=26) and triploids (2n=39). Diploids occur less frequently than triploids in this region. Their clonal populations are usually fertile owing to self-compatibility. The clonal populations of triploids are selfincompatible and usually sterile. Thus, the different self-compatibility is the main biological character distinguishing diploids from triploids. Pollen of triploids is viable in spite of meiotic irregularities in pollen mother cells (PMCs). Hybridization both between cytotypes and between the different triploid genets may take place, if they occur sympatrically. Offspring having diverse chromosome numbers between diploid and triploid level can originate as the consequence of such hybridization.