Karyotype variability in Pleurozium schreberi [Brid.] Mitt.

Significant variability in the karyotype od P. schreberi from populations in Poland was found, contrasting with high uniformity of the chromosome number. In 58 of 60 metaphases of gametophytes originating from three populations, haploid chromosome number n = 5 was counted. In two cells n= 6 was determined. In each metaphase the total and relative chromosome lengths and the arm ratio of the chromosomes were examined, and the chromosomes were ranked for these parameters. The haploid set consists of three chromosome types: metacentric, submedian and subterminal. Their frequencies in particular metaphase plates are different. The longest (A chromosome) and the smallest are highly stable in relation to the arm ratio, representing in the majority of metaphase plates the metacentric and submedian type, respectively. The A chromosome was polymorphic in respect to total lenght and the occurrence of secondary constrictions. Karyotype varied within and between populations. Eight types of karyotype were distinguished. Factors involved in karyotype variation are discussed.