This widespread diploid (2n = 20) of swampy shorelines ranges from southeastern states to tropical America. Based on their less robust annual habit, the more northern plants in eastern states have been segregated as P. repens var. fluitans (Ell.) J. Wipff & S.D. Jones, or even as a distinct species (Cr, W). However, some recent treatments have merged these two taxa (e.g. FNA 25, Y).