The purple plant is the lobelia cardinalis. The plant you think is Rotala indica, is not R indica. It does not have round leaves like that.
Lobelia cardinalis has purple leaves when it is grown above water. Underwater it turns solid green. There is also two forms of Lobelia: standard aquatic and small form aquatic. The small form is a true dwarf form and has smaller, rounder leaves. What you have is the standard form which will grow to be over a foot tall. What you got also has no roots formed. They are cut stalks instead of being rooted. I hope you have lots of light, because it will take very bright light for it to form roots, otherwise those stalks will just rot away at the bottom.
Where abouts are you? I wish people in this forum would fill in their location, at least what country or state they are in.
