Chromosome numbers and DNA content in some species of Mecardonia (Gratiolae, Plantaginaceae)

Cytogenetic characterization and determination of DNA content by flow cytometry of five species of Mecardonia Ruiz et Pavon, 1798 (Gratiolae, Plantaginaceae) was performed. This is the first study of nuclear DNA content carried out in the genus. Mitotic analysis revealed a base chromosome number x = 11 for all entities and different ploidy levels, ranging from diploid (2n = 2x = 22) to hexaploid (2n = 6x = 66). The results include the first report of the chromosome numbers for Mecardonia flagellaris (Chamisso & Schlechtendal, 1827) (2n = 22), Mecardonia grandiflora (Bentham) Pennell, 1946 (2n = 22), Mecardonia kamogawae Greppi & Hagiwara, 2011 (2n = 66), and Mecardonia sp. (2n = 44). The three ploidy levels here reported suggest that polyploidy is common in Mecardonia and appear to be an important factor in the evolution of this genus. The 2C- and 1Cx-values were also estimated in all the species. The 2C-values ranged from 1.91 to 5.29 pg. The 1Cx-values ranged from 0.88 to 1.03 pg. The general tendency indicated a decrease in the 1Cx-value with increasing ploidy level. The significance of the results is discussed in relation to taxonomy of the genus.