Ludwigia palustris	Ludwigia grandiflora	Ludwigia peploides	Mentha aquatica
leaves opposite	leaves alternate, leaf decurrent along petiole	leaves alternate, lamina and petiole clearly defined	leaves opposite, distinctly hairy
flower with 4 sepals, petals absent	flower with 5 sepals and 5 large (>1.5 cm) yellow petals	flower with 5 sepals and 5 large (>0.7 cm) yellow petals	flowers small, grouped, purple
leaf bracteoles inconspicuous	leaf bracteoles triangular, flat	leaf bracteoles roundish, swollen	leaf bracteoles absent