Neopolyploidy in Spartina pectinata Link: 1. Morphological analysis of tetraploid and hexaploid plants in a mixed natural population

Prairie cordgrass has been reported as a multi-polyploidy species having three cytotypes: tetra- (2 n = 4 x = 40), hexa- (2 n = 6 x = 60), and octoploid (2 n = 8 x = 80). A mixed-ploidy population comprising tetraploids and hexaploids was recently found at a single location in Illinois. However, adaptation and morphological differences between tetra- and hexaploids occurring in natural conditions as well as the contact zones of these cytotypes have yet to be determined. In this study, the cytotypes of 147 individuals of prairie cordgrass collected across the contact zone (4 x + 6 x ) were determined by flow cytometry using somatic G1 nuclei, and the results were confirmed by chromosome counts. Nineteen morphological characteristics were compared between the cytotypes. Tetra- and hexaploid plants have 2C genome sizes of 1.57 and 2.36 pg with chromosome counts of 40 and 60, respectively. This increase in polyploidy resulted in a greater variability of morphological expression in Illinois prairie cordgrass. Substantial differences in the flowering time, stomatal size, and plant morphological characteristics were observed between tetra- and hexaploids. The results indicate that the increasing of ploidy level in prairie cordgrass resulted in increased plant size in ploidy mixtures. The recent event of ploidy mixtures in prairie cordgrass natural populations offers unique opportunities for studying the formation and establishment of neopolyploidy.