Octopus Plant (Isoetes lacustris)

This is a fairly uncommon aquarium plant and is not always easy to maintain.  For some people it does quite well with a nutritious substrate, moderately soft water and moderate lighting, with or without supplemental CO2.  Other people seem to struggle with it, though the reasons are not always clear.  It's always worth a try though, because of it's strikingly different look in the aquarium.