Mystery Plant

John Nelson

This Mystery Plant may not look like a fern, but it is. Its presence in waters is a reminder not to dump out aquariums carelessly, because some aquatic plants can turn into pests.

Ancient, fascinating and very beautiful: a plant group that has always fascinated humans — the ferns.

Fern-like plants began appearing in the fossil record nearly 400 million years ago, and for a long period, they and their relatives dominated the landscapes, long before any seed-forming plants evolved. A large number of these fern-like plants were quite large, actually getting to be tree-sized. Very importantly, modern-day coal deposits around the world are the remains of uncountable tons of these ancient fern-like plants, which, after dying and decaying, were buried in sediments. Although they dominated these early landscapes, there are now only about 10,000 living fern species worldwide, well fewer than the number of flowering plants which we see around us.

All ferns, of course, reproduce from minute spores, rather than seeds. On most ferns, these spores are formed on the lower surface of a leaf (or “frond”). In some species, the spore-producing tissues are aggregated into scattered dots, each one called a sorus, which some people have mistaken as the result of a disease or insect infestation. Fern spores, once they reach the ground, begin a new plant that eventually will sprout characteristic leaves. But wait a minute — our Mystery Plant doesn’t look like a fern at all. But it is.

It is in a special aquatic fern family. The leaves float, of course; they are football-shaped, and covered on the surface by hundreds of very odd little hairs. The hairs are split into four nearly microscopic branches at the tip. (Get out your hand lens to see this.) The hairs form a very effective way to trap air, and so that if the little leaves every get turned over on top of the water, they eventually will right themselves, and all will be well again. This aquatic oddball fern doesn’t produce its spores in sori like the regular terrestrial ferns do, but rather in tiny little hard structures called “sporocarps,” which hang in the water under the leaves.

Our mystery fern is native to Latin America and the Caribbean but, like so many other plant species, has found its way farther north. Is seems to be happy as part of the Florida flora, and rather recently has spread to Louisiana, and even central South Carolina. It can be found on the surface of quiet water of canals, lagoons or swampy places. Although in the U.S. it is not common outside Florida, it is conceivable that this species could indeed continue on a more northern track, and even pose a threat as an invasive aquatic weed. (Another species in the same genus already has reached that unhappy status.) Please, folks, if you are an aquarium owner, never consider dumping its contents into a nearby body of water; that’s how many, many pesky aquatic species (plants and critters) have ended up being problems for us. And, if you are a fisherman or otherwise find yourself plying the waters of our lakes and rivers, consider washing your boat and motor before hauling it to a different waterway.

Answer: “Water spangles,” Salvinia minima.

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John Nelson is the curator of the A.C. Moore Herbarium at the University of South Carolina, in the Department of Biological Sciences in Columbia. As a public service, the herbarium offers free plant identifications. For more information, visit, call (803) 777-8196, or email

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