discus tanks

The current discussion of discus tanks reminded me of one set up I saw in
a German pet shop this summer:
The tank was approx. 48"x24"x24" large, and had 4 or 5 discus in it, 2 metal-
halides. The interesting thing about this tank were the plants: except for 
a couple of java ferns, there were none! BUT there was this beautiful growth
of algae that covered most of the decoration. It was about 5" tall, 
and dark-green. Unfortunately, I didn't have the time to  ask 
which species of algae this was. Does anybody have an idea?