Ludwigia uruguayensis

Ludwigia uruguayensis grows in dense colonies in wet soils, including swales between dunes and adjoining prairie ponds. Its leaves are narrow, tapered swords. The six bright yellow petals of its flowers slightly overlap. It is an exotic herb that is considered invasive in some areas.

References
Duncan, W. H., & Duncan, M. B. (1987). The Smithsonian guide to seaside plants of the Gulf and Atlantic coasts from Louisiana to Massachusetts, exclusive of lower peninsular Florida. Washington, D.C: Smithsonian Institution Press.

Nesom, G., & Kartesz, J. (2000). Observations on the Ludwigia uruguayensis complex (Onagraceae) in the United States. Castanea, 65(2), 123-125.