A single species, two basic chromosomal numbers: case of Lygeum spartum (Poaceae)

The existence of two chromosome numbers (2n = 16 and 2n = 40) in Lygeum spartum is confirmed in the Algerian steppe populations of Oran region. Chromosome counts were established for 11 Algerian populations and three supplementary populations from Italy, Spain and Greece. The karyotypes were characterized by chromosome markers obtained using fluorescence in situ hybridization and fluorochrome bandings. The organization of 5S and 18S-5.8S-26S (35S) rDNA was studied in both cytotypes. Six signals of 35S and 2 signals of 5S were observed in 2n = 16 population, while 10 signals of 35S and 4 signals of 5S were detected in the population with 2n = 40. All 35S loci were also strongly marked by chromomycin, but negatively stained by Hoechst, which indicates the presence of GC rich DNA in rDNA regions. The B chromosomes were found in both cytotypes, bearing a 35S locus in 2n = 16 population. Genome size, determined by cytometry of 10 populations, ranged from 9.27 pg for 2n = 16 to 26.63 pg for 2n = 40 populations. The sequencing of plastid and nuclear DNA markers did not reveal major differences among 2n = 16 and 2n = 40 populations. However, given the differences between two cytotypes and based on their morphological and cytogenetic characteristics, the 2n = 16 cytotype merits novel taxonomic treatment.