Just when you think you've seen everything, the web reveals a picture of a mushroom growing under water, producing bubbles of carbon dioxide. This picture is from the front cover of the latest issue of Mycologia (a scientific journal on fungi), and copied here from a lovely blog site called 'The Artful Amoeba - a blog about the weird wonderfulness of life on earth'.
The moss is producing bubbles of oxygen as it uses sun energy to turn carbon dioxide and water into sugars, but the fungus is doing what fungi do, and breaking down food storage products to get energy - carbon dioxide is a biproduct.
Its not that we didn't know fungi grew underwater. In 1984 I edited a field guide with the catch title of Aquatic cryptogams of Australia : a guide to the larger fungi, lichens, macroalgae, liverworts and mosses of Australian inland waters (published by Australian Society for Limnology).
In there are plenty of weird and wacky fungi that grow under water. However none of them are gilled mushrooms. The mushroom is one of the fruiting structures found in a particular group of fungi called the Basidiomycota (or basidiomycetes). Within this group, the gilled mushrooms are commonly called the agarics.
Despite the fishy adjective, we expect to find gilled fungi in paddocks, forests and supermarkets, not underwater. So the record of a genus called Psathyrella fruiting regularly in the Rogue River in Oregon, USA, was worthy of some fanfare.
There was, and perhaps still is, some scepticism around this discovery. The authors of the paper watched this fungus over a few months to make sure it didn't just produce one mushroom that happened to be flooded by water. Over 11 weeks the fungus produced its fruiting bodies underwater, always fully submerged. It also has a distinctive shape and form, as well as characteristic DNA sequences, so it's a new species of Psathyrella, presumably adapted for this odd habitat.
The fungus grows along half a kilometre of the river, above and below a waterfall, so the authors conclude it is not a single clone or colony.
The next test for the researchers is to try and grow the fungus in the laboratory, both underwater as well as above.
As always when you find something in a river, people ask how does it get upstream. I get this question about the freshwater red algae I study, which typically grow on rocks in small mountains streams.
In the case of the fungus its been suggested aquatic invertebrates and other animals carry it around. Perhaps its dispersal relies entirely upon animals. With algae, sometimes aquatic birds are suggested. Alternatively, for groups with a long evoluntionary history they may evolve in a swamp or waterbody that ends up moving and flowing in various locations. As long as it remains firmly anchored, the world moves around it...
Part of the surprise of this discovery was that previously no one had looked underwater for mushrooms. It had been assumed they wouldn't be there - floppy, gilled fruiting bodies didn't seem to be well adapted for this habitat. Fungal foragers will now have to don their togs, bathers, swimmers or cosis (depending on what part of the world, or Australia, they live in...)