Ludwigia octovalvis
[Primrose Willow]
This plant has larger yellow flowers, with petals about 2 to 4 mm long when compared to a similar looking plant with smaller flowers, named L. hyssopifolia. The petals of L. hyssopifolia are about 1 to 2 cm long. The plant below should be the same plant although it is covered with tiny hairs and has broader leaves.