Cryptocoryne is an Asian genus of amphibian plants, familiar to aquarists, but not really grown by anybody else. This one comes from central Sri Lanka, and prefers
tropical conditions, but I thought it was worth a try in the greenhouse - the strangest things sometimes turn out to be cold tolerant.
Grown submerged in the aquarium they will produce nothing but leaves. They have to be allowed to grow emersed to produce flowers. They are generally produced as emersed plants, and then submerged at the point of sale. I am hoping that a shallow covering of water will provide adequate protection.