If you are looking for a completely bomb-proof stem plant that grows under maximally abusive conditions, hygrophila polysperma might be your best pick. I picked this up from Maidenhead Aquatics without knowing anything about it other than it looked pretty in the store. I wound up planting it in a mix of Aquasoil overlayed on Biohome biogravel and this plant thrived. Doesn’t need CO2, doesn’t need much light, doesn’t need any fertilizer, in other words, perfect for a low-tech tank setup.
Why don’t I have it anymore? Well… I switched to a high-tech tank setup with injected CO2 and brighter lighting and the hygrophila went ballistic. Every week I had to cut off and throw out huge chunks of it, it grew so fast. It also got a bit leggy, and rooty and wasn’t the most pleasant thing to look at, which combined with its high maintenance meant I decided to get rid of it.
Great plant for setups when absolutely no other plant can make a go of it.