Rotala pusilla (to be confirmed)

Some of them in the photo are another species, while I think most of my friends here can still recognize it. The R.pusilla is the ones with broader and greenish leaves.
This scientific name is used by most of Japanese aquarists, some books even say that it can be found in Japan, while I doubt this because it seems to be a tropical plant, and I can't find this name in formal botanic publications regarding aquatic plants in Japan. Perhaps the description made by the RVA website (http://www.rva.ne.jp/main.htm) that it is from the South America is more acceptable to me, can anyone confirm this for me?