Waterlogged areas can be a headache for many gardeners as they can be expensive to improve for growing plants that demand a well-draining location. Ever since I joined the National Parks Board (NParks) and got stationed in HortPark (the gardening hub of Singapore), I got to face the challenges of having to plant up waterlogged areas. One of the plants I got acquainted with was Hydrocera trifolia, commonly known as the water balsam or marsh henna. My colleagues from the Hort Management section planted a grove of Hydrocera trifolia in a waterlogged area near the prototype glasshouses located near the back of HortPark.
Hydrocera trifolia is native to lowland areas stretching from Southern India, Sri Lanka, southern China, Indo-China, Thailand, Peninsular Malaysia to Indonesia and is found growing in ditches, pools, rice fields and marshy places. From its ability to grow in stagnant water and the picture of its flowers shown above, it is clear why Hydrocera trifolia is called a water balsam. According to a Kew Bulletin paper by Grey-Wilson, this plant can grow in water with its stems submerged in water to a depth of 70 cm! For those of us who are familiar with the common garden balsam, Impatiens balsamina, it is a plant that loves to grow in moist areas but never waterlogged!
This plant is a perennial and can grow up to 1 m in the tropics. The part that grows above water is leafy and unbranched and its stems are held erect. Interestingly, the submerged portion do not have leaves and will thicken and become spongy, which I think is an effort by the plant to prevent itself from sinking! How interesting!
However, Hydrocera trifolia and Impatiens balsamina differ in two ways, in terms of the structures of their flowers and fruits, according to Grey-Wilson. In a Hydrocera trifolia flower, one will be able to observe that there are five sepals and petals, where the latter are all free from one another. In Impatiens balsamina, the flower usually have 3 sepals and the four petals instead come in two pairs, with the dorsal petal free.
The fruits of Hydrocera trifolia do not split open like those found in Impatiens balsamina which we learn from primary school textbooks that they burst open when ripe to disperse seeds via explosive action. Each fruit of Hydrocera trifolia contain about 5 seeds whereas one can find many more in Impatiens balsamina.
Like Impatiens balsamina, the flowers of Hydrocera trifolia yield a dye and the flowers of the latter are used to prepare a red dye for fingernails which serves as a substitute for henna (Lawsonia inermis). This use is behind Hydrocera trifolia’s alternative common name, water henna.
This plant is easy to grow that are suited for growing inside or near the edge of ponds. Although aquatic in growth habit, one can also grow it in a pot of soil that is kept moist at all times. It thrives in semi-shaded areas to locations with full sunshine and can be propagated easily via stem-cuttings or via layering.