Background plants
I have didiplis growing in my background, it's over 30" long and very bushy, but it took a few months to get that tall. I recently got Potamogeton (ssp) from albany aquariaum. In their show tank it has 6" long .5" wide leaves that float vertically from a stem every couple inches. From a distance it looks like some sort of vals, but up close you can see it's a stem plant. Since it's a stem plant it'll probably fill in fairly quickly compared to vals and especially crypts. One of the cuttings I got also had some sort of flower stamen that looks like the center of an anubias flower so I expect more of those.
I broke off a piece with one node and buried it, now there's a small plant there, so the stuff is quite hardy and suitable for a beginner. Apearantly it also sends out runners that make new plants every few inches.
I don't know what subspecies it is, there is one called p. crispus that is mentioned for aquaria, but mine has straight long leaves.