While messing around in New Orleans, TPP happened to visit a water garden nursery, a big one, just to see what they had. Among the nice array of water lilies were some of the biggest water ferns TPP has ever seen, which is not to say he had never seen this fern before, but not this big. Many people grow "water sprite" (Ceratopteris thalictroides) as a submerged aquatic fern and it has finely disected leaves and is usually of modest size, probably a combination of being submerged and in lower light. It also grows as a floating plant. This according to an A#1 correspondent is more likely Ceratopteris pteridoides, a larger and more robust plant. The leaves get much bigger. Some of the leaves are broad, merely lobed, and thicker, and on older plants bearing plantlets upon these leaves (asexual reproduction). The petioles enlarge and become robust, inflated, probably filled with aerenchyma, a ground tissue with lots of intercellular spaces, functioning as floats sort of like the floats of water hyacinth. Some of their ferns spread their fronds more than a foot from the center of the plant forming semi-globular shape over two feet across. Their recommendation, "better have a big pond". This fern has some potential for student research as it obvious can grow fast under high light conditions, and it has both sexual and asexual reproduction, as well as bimorphic leaves. They basically gave me a small plant. It's in our lily pond now, and were this a warmer climate, and if this fern were not already loosed upon our ecosystems in places like Louisiana, TPP would worry. (Sorry, even the Flora of North America is unclear about whether is a native or naturalized species.) No biologist wants to be responsible for releasing a fast-growing invasive species, but this tropical fern won't survive up here even if it were to get free of our pond. It'll have to be overwintered in our university glass house. Our cooler climate will slow down its growth, so it will be interesting to see how big it gets in what's left of our summer.