Sampling
A set of 146 coarse-textured P. vaginatum , 18 fine-texturedP. vaginatum and 10 P. distichum plant samples was
collected along the Atlantic and Gulf coasts of the southeastern United
States, from North Carolina to Texas, during June and July of 2016 and
2017 (Fig. 1A; Table S1). Collection habitats included beaches, salt
marshes, brackish estuaries and freshwater rivers and lakes. To reduce
the chance of repeatedly collecting representatives of the same clone,
localities were separated by at least 1.5 km. One to three samples were
collected in each location. When multiple samples were collected from a
single locality, they were separated by at least 100 m to minimize
replicated sampling of a single clone. Samples were harvested as stolons
which were wrapped in a damp paper towel and then placed in a plastic
bag for no longer than one week before planting. Stolons were propagated
in the Donald Danforth Plant Science Center greenhouses. In addition to
the wild-collected material, a set of 40 samples, representing 35P. vaginatum (two of which are coarse-textured) and five P.
distichum , were obtained from the USDA National Genetic Resources
Program. Additionally, dried tissue for DNA extraction, representing
four P. vaginatum accessions and one P. distichumaccession, were acquired from Uruguay from Dr. Pablo Speranza
(Universidad de la República de Uruguay).