Milfoil (Myriophyllum aquaticum) grown emersed?

The Myriophyllum aquaticum is doing quite exceptional under the 250w MH
and has reached a length of about 3 feet. I had already chopped the tops off
this and replanted them. I notice the leaves do not resemble the original
shape in either of my tanks. When I first put it in the 49 gal. the leaves
were highly divided and fairly short (somewhat like feathers?). Now the
leaves are branched nearly so much and are many times longer. I'll try
to diagram a leaf below. Is it possible that these plants were grown emersed
at the plant farm? What might account for the difference in leaf shapes?
The original leaves turned reddish brown and look dead. The new leaves are
greenish to golden-green in bright light. Quite attractive :-) (bragging

     _\| |    old ones, about 8x oversize

     \ \ | / /
      \ \|/ /
     \ \ | / /  new shape, similar scale
      \ \|/ /
       \ | /

 - Steve