Re: Isoetes

Isoetes is an interesting plant. First, its a fern with the sporangia 
located at the base of the leaves. Second, Isoetes get much of their CO2 
the sediment through the roots. To do this they have a large root:shoot 
ratio and lots of aerenchyma. Third, Isoetes is a CAM plant which means 
that it can fix CO2 at night by forming C4 acids and then reduce the CO2 
in the following light period. Isoetes is usually found in acidic lakes 
or vernal pools that are extremely carbon limited.
To successfully grow the plant you need acidic water, low light and a 
substrate which is enriched with either clay or some soil to supply CO2 
to the roots. At our local university Isoetes has been grown for years in 
a small 10g aquarium with no overhead lights (its in a dark corner of the 
greenhouse) and a soil/sand substrate. Every year or so the greenhouse 
operator throws in a handful of potting soil to renew the sediment. The 
plants are in great shape. Having said that, Ive tried at home to grow 
the same plant and have had no success ... my light is much higher, I 
have an alkaline pH, and 2 inches of plain gravel over my soil substrate. 

Good luck, Dr. dave