Around 10 stems of vallisneria, similar to what's pictured here.

This is a great plant that does well even in hard water. Super easy to keep and fast growing.

I would consider this a good starter plant - it's not as easy as java fern, anubias or buce, but it's as easy as any stem plant. It does like a bit of ferts from time to time (especially around the roots). I find that it grows best in sand or fine clay, it doesn't seem to like flow around its roots.