Karyotype characterization of four Mexican species of Schoenoplectus (Cyperaceae) and first report of polyploid mixoploidy for the family

Abstract

Karyomorphological analysis of four species of Schoenoplectus (Cyperaceae) from north-central Mexico were carried out. Chromosome numbers ranged from 2n = 38 to 2n = 84. New records of counting are given for Schoenoplectus acutus var. occidentalis (2n = 38 and 2n = 84) and S. americanus (2n = 66). Intra-individual variation in chromosome number is reported for the first time for S. acutus, with a rare polyploid mixoploidy with a prevalence of cells with 2n = 38 (36 small + 2 compound, larger chromosomes) and a few cells with 2n = 84 small, dot-shaped chromosomes, this being the first record of polyploid mixoploidy for Cyperaceae. Mean length of the diploid set ranged from 51.5 μm (S. tabernaemontani) to 79.5 μm (S. acutus). The lowest average chromosome length for the dot-shaped chromosomes was 0.69 μm (S. acutus) and the highest 1.62 μm (S. tabernaemontani); the pair of large chromosomes in S. acutus reached 3.17 μm. A low interchromosomal asymmetry index (A2), 0.11 to 0.14 was found, very similar among all the species except for S. acutus (A2 = 0.30). Absence of primary constrictions was confirmed. The most common mechanism of karyotype variation in the studied species is dysploidy, followed by polyploidy. A comparison of chromosome numbers between Schoenoplectus and the recently segregated Schoenoplectiella based on the literature reveals that Schoenoplectus has higher numbers (n = 18 to 64; 2n = 36 to 84) than Schoenoplectiella (n = 5 to 44; 2n = 18 to 76) as well as a higher prevalence of disploids.