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Georgia Journal of Science

Article Title

POLYPLOIDY AND GENOMIC VARIATION IN NORTHERN FLORIDA AND COASTAL GEORGIA POPULATIONS OF RHEXIA, A SMALL GENUS OF FLOWERING WETLAND PLANTS ENDEMIC TO THE NORTH AMERICAN COASTAL PLAIN**

Abstract

Rhexia, a small genus of flowering plants with 13 species commonly known as meadow beauties, occurs primarily in the North American Coastal Plain (NACP), a region identified in 2016 as the world's 36th global biodiversity hotspot. The evolutionary history of these wetland plants is complicated by repeated hybridization and allopolyploidy events, as evidenced by differing phylogenies of maternal vs. bi-parentally inherited molecular markers. Genome duplication (autopolyploidization) is also common in Rhexia, with a third of the species occurring as polyploid complexes (e.g. in R. nashii n=22 or 33). Thus, this small yet genomically complex group of flowering plants can serve as a model for the study of evolutionary processes in plants of regions with high biodiversity coupled with habitat instability, such as the NACP. Our main goal was to determine cytotypes of differeng ploidy levels from specimens representing various species of Rhexia by counting chromosomes in root tip meristem cells, to provide calibration standards for efficient genome size estimation using flow cytometry for future, more extensive studies. Living specimens of 143 Rhexia plants comprising five Rhexia species and two putative hybrids were collected from 21 populations in northern Florida and coastal Georgia, and reared in greenhouses. Root tips were harvested during the growing season, immediately pretreated with 8-hydroxyquinoline to enhance spreading of mitotic chromosomes, fixed in 3:1 ethanol-glacial acetic acid, and stored in 70% ethanol. Root tip meristem cells were isolated and squashed on glass slides, stained with aceto-orcein or DAPI, and examined via light and fluorescent microscopy. Discrete cells with well-defined chromosomes were imaged and counted. We expect to establish cytotypes for multiple specimens of each represented species for varying ploidy levels, thus providing reliable standards to later be used for cytotyping via flow cytometry.

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