Roundleaf toothcup originates from Southeast Asia, southern India and Japan. The species name rotundifolia means round leaves. But this only applies to the marsh variety, which has circular leaves. In aquariums Rotala rotundifolia has long, thin leaves. Commonly found in North-East India, it is a perennial herb with stems usually branched, erect, floating or creeping, to 30 cm long. Stalkless leaves are broadly elliptic to circular, to 1.2 cm long. Bracts are ovate, obtuse, to 4 mm long. Pink flowers are nearly stalkless, in prominent many-flowered racemes. Sepals 4, triangular, to 1 mm long. Petals 4, inverted-egg shaped, 2-3 times as long as sepals, mauve. Capsule is spherical, about 1.5 mm in diameter.