Hi all,
Ollie a lot of the problem with real "black water" is the extreme acidity and very low nutrient levels. Most Black water rivers don't actually have any true aquatic vegetation, just dead leaves and wood, which are very slow to degrade in these extreme conditions. If you want a real "Rio Negro" biotope you are probably going to struggle to find S. American plants, although
Echinodorus species would naturally grow in the flooded forest, which would become a black water lake for some part of the year. Wit enough light some species of
Cabomba and
Myriophyllum will also grow well.
If you are not so bothered by provenance and just want plants that will grow there is more of a range. Other than plants like
Vallisneria and
Ceratophyllum most plants will grow even at very low pH and nutrient levels, but they will mainly have low growth rates.
I would think all 3 of your choices will grow, although for example
Eleocharis acicularis likes hard water. Other plants that I've grown in acid water are
Anubias, most mosses and ferns, many other
Cryptocorynes <
http://www.xs4all.nl/~crypts/Cryptocoryne/>,
Heteranthera,
Isoetes,
Utricularia gibba and
Blyxa.
Although I'm sure people will add many more.
cheers Darrel