Alternanthera sessilis is an aquatic plant known by several common names, including ponnanganni(in Tamil), Mukunuwenna(in Sinhalese) sessile joyweed and dwarf copperleaf. It is used as a vegetable specially in Sri Lanka and some asian countries.

The plant occurs throughout the tropical and subtropical regions of the Old World. It has been introduced to the southern United States, and its origins in Central and South America are uncertain.
This is a perennial herb with prostrate stems, rarely ascending, often rooting at the nodes. Leaves obovate to broadly elliptic, occasionally linear-lanceolate, 1-15cm long, 0.3-3cm wide, glabrous to sparsely villous, petioles 1-5mm long. Flowers in sessile spikes, bract and bracteoles shiny white, 0.7-1.5mm long, glabrous; sepals equal, 2.5-3mm long, outer ones 1-nerved or indistinctly 3-nerved toward base; stamens 5, 2 sterile. In the wild it flowers from December until March.
Aerva lanata is often mistaken for Alternanthera sessilis, which is also of the Amarantheceae family, and looks similar. On careful observation you will notice that flowers of Alternanthera sessilis are situated over the stem and their shape is round. As its flowers look like the eyes of a fish, Alternanthera sessilis is called Matsyakshi, fisheyed. Other Indian names of this plant are Koypa in Marathi, Honganne in Kannada, Ponnaganti koora in Telugu, Ponnanganni Keerai in Tamil pennai in Malayalam. The plant is known as "Mukunuwenna" in Sinhala. The plants are shredded finely and stir fried with grated coconut and spices to make what is known as "Mukunuwenna mellum".
The plant grows wild, but is also cultivated for food, herbal medicines, as an ornamental plant (red variety, as a hedging plant), in the aquarium trade (though it only grows submersed for short periods), and as poultry feed.
In certain regions of South East Asia, the leaves and young shoots are consumed as vegetables. in Karnataka, Andhra Pradesh and Tamil Nadu, the leaves, flowers and tender stems are consumed as vegetables.
As a herbal medicine, the plant has diuretic, cooling, tonic and laxative properties. It has been used for the treatment of dysuria and haemmorrhoids. The plant is also believed to be beneficial for the eyes, and is used as an ingredient in the making of medicinal hair oils and Kajal (kohl).
This species is classified as a weed in parts of the southern States of the USA. It is usually (but not always especially in areas of high humidity where it can even be a garden weed) found in wet or damp spots.