Looks like java moss to me. Was the pic taken from your aquarium? I only ask because if it is, the moss should do well, considering nice growth from plants in background.
To give you an idea of java moss growth rate...this is under high light with CO2. Twelve days growth period:Thanks a lot. But I have a problem with my moss....it doesn't grow at all. It might be growing very slowly but java moss is supposed to grow fast isn't it? What is the growth rate of this moss?