Neptunia oleracea is the aquatic equivalent of the common sensitive plant (Mimosa pudica). Commonly known as the water sensitive plant, it grows via long stems and sports the same pinnate leaves like its terrestrial counterpart, which closes up when disturbed.
Unlike the common sensitive plant, Neptunia oleracea does not have thorns and produces flowers that are yellow in colour rather than pink. Interestingly, the mature stems of Neptunia oleracea that are in contact with water develop somewhat differently as they will have a layer of white spongy tissue around the stems formed between the leaves to help them float on water.
Because of these characteristics, I find this plant an ideal and interesting candidate to show as an example to children of a plant that moves, much like the common ones that we now know that include the common mimosa, the dancing plant (Desmodium gyrans) and Venus fly trap (Dionaea muscipula). Without thorns, Neptunia oleracea is safe to handle by children and what’s more, its a mimosa that wears a float to swim in water! It is an edible plant too and children can cook it as a fun activity!
According to Plant Resources of South East Asia (PROSEA), Neptunia oleracea is widely distributed in the tropics of both hemispheres but the origin of the species is uncertain. It occurs wild and cultivated as a vegetable throughout South-East Asia, particularly in Thailand and Indochina. Neptunia oleracea can be found growing in inundated ricefields and in other fresh water bodies and sometimes becomes a weed which choke up waterways in some countries. A member of the bean family, Fabaceae, this plant has nitrifying capability and releases nitrogen into the water.
In Singapore, this plant is not easily found, perhaps due to the fact that our country has been urbanised to a great big extent and all our waterways have been cleared and paved with concrete over the past few decades of rapid development. It cannot be purchased from local nurseries as well. I managed to find some on sale in a Thai supermarket in Golden Mile Complex, which is known here as the ‘Little Thailand’. Stems of this plant of about 30 cm are sold in bundles. It is best to buy them when they first arrive before they dehydrate over time.
The fresh stems of this plant can be used for propagation. After several tries, I succeeded in propagating Neptunia oleracea and what I did was to simply throw the stems into a pond. The stems rooted rather quickly and the plant started to extend its stems in just a week in water! Plants are best grown inside a pond that is exposed to full sun or semi-shade. Now I have some being grown in the natural pond located nearby HortPark’s Kampong Daze theme garden.
Do you know that the roots of this plant are used medicinally? The people of Kelantan, Malaysia) use the root as an external remedy for necrosis of the bones of the nose and hard palate. The juice of the stem is squeezed into the ear to cure earache and the root is used in the advanced stage of syphilis in Malaysia. An infusion of its roots is rubbed all over the body with rice flour to reduce fever. A common ingredient of Thai cuisine, the leaves and young shoots are said to have a nutty cabbage-like flavour and can be eaten raw (such as after being dipped in sambal blachan) or cooked (added to soups).