Neptunia plena common names include Water mimosa, Water dead and awake, Water sensitive plant.
Water mimosa is an aquatic plant that attaches to the bank at the waters edge and sends down a taproot. It has a special ‘fibrous sponge’ to float. Leaves are olive green and are arranged in opposite pairs along the stem and when disturbed or touched the leaflets close up.
Water mimosa flowers are yellow ball-shaped. Neptunia plena is planted or occasionally escaped in wet places and native to tropical Americas.
Source: Wikipedia ~ Neptunia oleracea