It came from a friend who visited Tropica in Denmark. It was in one of their display tanks as a test plant they decided not to use in their line-up for one reason or another. It's almost certainly a variety of mexicana.
You won't find much info on it because outside of the few people who bought it on here or APC from the few of us who have it not many people have heard of it.
It's pretty easy to grow. I've not had the same issue with topping it. I always top my Rotalas and leave the bottoms to regrow.
In the D.C., Maryland, or NOVA area? Come check out The Greater Washington Aquatic Plants Association! www.gwapa.org