Basic cytogenetics in Cymodocea nodosa (Ucria) Ascherson from Mediterranean Sea (Sicily, Italy)

Cymodocea nodosa (Ucria) Ascherson is the only representative of the family Cymodoceaceae growing in the Mediterranean Sea. It is also present along the coast of North Atlantic from Portugal to its southern limit in Mauritania, as well as in the Canary Islands and in Madeira. Observations on mitotic divisions and chromosomal behaviours as well as DNA measurements have been carried out on populations from Sicily. Standard chromosome counting and Image Cytometric analyses were used to determine the chromosome numbers and the ploidy of each population. Intra-population differences in somatic chromosome number were reported in this species. Cytotypes 2n=14 and 2n=28 were observed in C. nodosa from Le Brusc (France). Recently, similar chromosome variations have been described for two of the three other species known in this genus, C. angustata Ostenfeld and C. serrulata (R. Brown) Ascherson et Magnus. The third species, C. rotundata Ehrenberg et Hemprich ex Ascherson, has a chromosome number of 2n=14. Our data show the presence of high chromosome number variation in individuals from all the studied populations, even in a single root. Near the apical meristem the chromosome numbers were lower, while further from the apex they were higher. Mitotic anomalies were also detected. The relative DNA value of nuclei confirmed that all of the studied populations presented polysomaty. Cytological and cytometric data clearly indicated that the combined action of endoreduplication of chromosomes and aneusomaty were involved in this cytogenetic behaviour. The data reported represent the first contribution to understanding the basic cytogenetics in this genus.