From Aquarium Plants - Christel Kasselmann:
Rotala rotundifolia
(Roxburgh) Koehne (1880)
Family: Lythraceae.
Synonyms: Ammania rotundifolia Buchanan-Hamilton (1820), and others.
Etymology: Rotala: see Rotala macrandra; rotwulifolia: round-leaved.
Distribution: Southeast Asia (India to Japan).
Description: Marsh plant with creeping, ascendent or drifting shoots, up to about 70 cm long. Emersed leaves decussate, sessile or short petiolate, entire, obovate to round, about 1( — 2) cm long, upperside olive green, underside slightly reddish. Submersed shoots erect, very branched.
Leaves opposite or in 3-4-merous whorls. Blade lanceolate, in drifting shoots also almost round, up to 2.2 cm in length, upperside olive green to reddish, underside pale to a strong violet color.
Inflorescence densely flowered, at the base often branched raceme, up to 11 cm petiolate. On each node, 2 flowers with a cordate or almost round up to 6-mm thick bract. Solitary flower short petiolate. Calyx with 4 triangular calyx-lobes without appendage. Bracts about 1 mm; 4 petals, pale purple, obovate, about 1.5 mm long; 4 stamens, about 1.5 mm long, not longer than the calyx-lobes. Style 0.5-1.5 mm long; stigma capitate. Ovary globular. Capsule about 1.5 mm, with 4 valves opening. Culture: An especially recommendable, adaptable, decorative and quick-growing stem plant, good lighting is necessary to achieve strong, reddish shoots. The species will tolerate large fluctuations in hardness and pH-values. Optimum temperature range is 24-28 °C. Propagation is unproblematic through lateral shoots. The plants do not display good protruding growth from the water so that adaptation to emersed cultivation is not easy. However, once this has been established cultivation in the paludarium or greenhouse is so rapid that the species can become a real weed. Inflorescences occur only above the water surface.
Ecology: The species grows in marshy areas and often in cool mountain regions, in China up to an altitude of 2650 m.
Other: Was introduced in 1960 as Rotala indica. This, however, is a different species.
And From the Complete Guide to Water Plants - Muhlberg:
Rotala rotundifolia (Roxb.) Koehne
The species was named Ammannia rotundifolia by Roxburgh in 1820. Koehne moved it to the genus Rotala in 1880. In aquaristic literature it is often denoted as R.indica, but this is an error.
Distribution: South-east Asiatic mainland.
Characteristics: A herbaceous plant with elongated shoot axes and leaves arranged opposite and decussate, creeping horizontally on wet soil and growing erect submerged. Leaves sessile. Submerged leaves very variable, linear, lanceolate, blunt, elliptical, egg-shaped or almost roundish, up to 1.5 cm long and up to 4 mm wide, upperside pale-green, underside whitish-green to reddish. Aerial leaves always round, dark-green. Inflorescence is composed of several spikes, terminal. Flowers small, with red petals of the corolla.
Cultivation and Propagation: A small-leafed, undemanding plant, to be used in a clump among larger plants in the middle part of the tank, but it also looks well in the background. It is equally suitable for being planted in the corners of the foreground. In an aquarium shoots often grow creeping along the substrate and branch intensively. This species should not be too much in the shade. Temperature just above 18 °C. Propagation from cuttings.
Rotala indica (Willd.) Koehne
The species was named Peplis indica by Willdenow in 1799 and moved to the genus Rotala by Koehne in 1880.
Distribution: South-East Asia; it has become naturalized in the rice fields of northern Italy.
Characteristics: Herbaceous plants with elongated shoot axes, creeping horizontally on wet soil or growing erect when submerged. Leaves arranged opposite and decussate, sessile. Submerged leaves linear to slightly spatulate, up to 1 cm long and up to 3 mm wide, upperside pale-green, underside whitish-green. Flowers solitary in leaf axils of aerial shoots, very small with pink petals of the corolla.
Cultivation and Propagation: As described for R. rotundifolia. However, the species does not grow satisfactorily everywhere.
More on the 2 species from others:
Rotala rotundifolia produces flowers on terminal spikes (racemes) and differs from a previously introduced species, Rotala indica, which is an annual species with shorter, lateral flower spikes.
Rotundifolia flowering (Photo: Muhlberg - The complete guide to aquarium plants)
Dennis
Rotundifolia can have 2 or more leaves per node (notice bold reference in Kasselman) it seems I have the 3 leaf variety
Carlos
The 2 plants I have here are easily differentiated even on the same tank.
Both leaf shape and color.
R. indica<--> R. rotundifolia is there a difference? 
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