I have Marsilea from you that I put in two different tanks, one El Natural and one with fluorite substrate and DIY yeast CO2, and in both they have grown pretty much the same. Some leaves are slightly larger and taller than the others, but pretty much all low growing. I was surprised that a few leaves have sprouted in the four-leaf clover form in the El Natural tank. I had thought that would only happen if it was growing emersed. And these weren't the plants you sent that had been floating to encourage submerged growth.
I recently read an article in Tropical Fish Hobbyist magazine on Marsilea. The author wrote that Marsilea growth can be variable depending on growing conditions. Apparently when grown outside in the sun it can grow long stems that float on the surface. It sounded like the author had Marsilea send leaves to the surface in an aquarium when it was overcrowded, but otherwise usually it would grow in the familiar short groundcover fashion. She also said she had it grow in the four-leaf clover form in low light areas shaded by other plants, but mine is front and center with nothing else to block the light.
I'm sorry I can't say much about ferts, the subject pretty much baffles me
. I just wing it and have had pretty good luck with the tank that I add ferts to, but I have found that I can't dose iron without getting hair algae either. That's one of the reasons why I went with El Natural on my other tank.
Anyway, I love the plants (thanks again) and for someone like me who isn't overly concerned about aquascaping, I think its kind of interesting that you never know what you're going to get from them!