Okay, here is what I know from recent experience. About six weeks ago I bought six stems the australis variety.
In my medium light tank(2.5 wpg) with co2 and ei dosing, the leaves are growing very small and have turned a light yellow green (not sickly looking though) and the stems are growing sideways.
In my low light tank with ferts, the stems are growing sideways, the leaves are big, and one of the stems is totally horizontle but it has three new stems growing out of it now. They are a nice pale green.
In the totally lowlight tank with only fish fish poo for fertilizer, they are growing really tall but with aren't leggy looking.
I understand it is very tolerant of salt, but I don't salt my tanks.
Hope this helps