What's this plant & Riccia fluitans

Greg. Tong wrote:

>On page 24 of Amano's book, Nature Aquarium World, there's a plant in the
>background that I have but can't name. It's the long stringy green plant
>with short spiky leaves that is curving toward the center of the photo.

I think this is a Myriophyllum, Water Millifoil. At least it looks similar to
the one I bought recently.

Mike Eckardt wrote:

>The most common is R. fluitans, which is a floating plant and doesn't do
>well submers for an extended period of time without a lot of  maintenance. 
>Theother species looks exactly the same, except it sinks and has adapted to
>submers living conditions. I, as well as others on this list, suspect that
>Amano uses this species in his tanks.

This observation is interesting, because Windelov's book , which I have,
"..... The forms growing in bright light or the partly emersed forms have a
wider thallus and are brighter green in color; sometimes they are mistaken
for other species. ..... Some parts of the thallus often sink to the bottom
of the tank and form very decorative ball-shaped tufts. ......."  Did I
misunderstand something here, or is there both a floating and submersed form
of Riccia fluitans? I have anchored several tufts to my substrate in a 10
gallon, I'm setting up as a NWA style aquarium. I have noticed that the color
has changed slightly getting brighter and the new thalli have widened in the
older tufts.
 I didn't understand the word thallus, so I looked it up in a dictionary.
thallus : a plant body that is charactreristic of thallophytes, lacks
differentiation into distinct members (as stem, leaves, and roots), and does
not grow from an apical point. 
Personally I'd like to read more discussion here about these interesting
PacNeil at aol_com[Neil Schneider]