Assuming the identification as Rumex dentatus is correct, this seems to be a first record for Florida. This is not completely unlikely, as it has been found in a number of US states and is well established in southern California and Arizona. The characters seen here match the FNA description closely, such as the elliptic-lanceloate leaves with undulate edges, and the inflorescences spread out on long straight stems, and of course the teeth along the tepal margins; I don't see any of the known Florida species having all of these.

The specific location of this population is a low area draining from the solar farm to the west; possibly the seeds hitched a ride on construction materials or machinery coming from elsewhere.