Just want to point out the history and care of this little species, which is gradually spreading throughout the hobby.
In the spring of 2004, one of my Brazilian friends sent me a 'test' package including two new stem plants. He labeled both as Rotala sp. "Rio de Janeiro Botanic Gardens" (one was #1 and the other was #2). Why the name? Both were first collected growing submersed in the botanic garden of that city.
The first of these 'Rotalas' seems to actually be Rotala, with identical growth form and appearance to Rotala rotundifolia "Green" save for the fact that it has a more creeping habit. It is potentially a new foreground plant.
The second was definitely not a Rotala, and I finally got to identify it as belonging to the genus Hedyotis. This lanky, minute species has very narrow green leaves and long internodes. Under high light, it will grow more horizontally much like Rotala rotundifolia "green." It is a very brittle plant, which it uses to its advantage by shedding sideshoots throughout the tank with the slightest touch. It is definitely an oddity. I do not know the exact species name, but for now I am comfortable to just call it Hedyotis sp. "Rio" until we get the species name.
Greg probably has the best picture, here: