Back to nature

I was curious about something.  We've tossed around the natural 
environemnt thing (well, Stephen brought it up and I tossed it :-).

Concerning nature environments:

TOA states that Crypts typically come from "laterite streams".

South American plants come from muddy streams or swamps with decaying
leaf matter (I suppose).

Does anyone know what other types of natural environments various 
species are found in?  Anubias (clean, sandy streams?), Aponogeton?
Rotala? Luwigia? 

What plant species are found in "vermiculite streams"?