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.
Common Name: Octopus plant
Family Name: Isoetaceae
Native To: Southeast USA
Lighting: Moderate
Requirements: Can be touchy
Growth Form: Upright
Growth Rate: Moderate
True Aquatic: Yes
Placement in Tank: Mid ground accent
Available As: Bare root