Psathyrella aquatica

It was found by Southern Oregon University professor Robert Coffan in the Rogue River in the U.S. state of Oregon.[1] Coffan and his colleagues, Darlene Southworth and Jonathan Frank, found the mushroom in 2005. The biology department at Southern Oregon University confirmed that the mushroom was a unique discovery.[1] Once their research was published, it was named one of the most significant species discovered in 2010.[2] They have so far been discovered in a 1 kilometer stretch of the river, and have an observed fruiting season of mid-June to late September[3] Many scientists were skeptical about describing this mushroom as a new species because of the hundreds of similar looking species in the Psathyrella family.[2][4]

Less than 1% of aquatic fungi are assumed to be discovered yet, and many are assumed to be microscopic, with only a small fraction thought to produce fruiting bodies.[5]

The fruiting body consists of a small convex cap and a long stipe.[1] Its cap is brown, convex, and has gills underneath.[1] The young mushroom develops a veil, which is lost as the mushroom grows to maturity.[1] The mushroom's stipe appears to be quite strong, and is anchored up to 1.6 feet (0.5 m) deep in sediment, in order to stand up to the fast-moving river currents where it is primarily found.[1] The stipe is covered in thin hair like structures.[1] Spores released by the gills stay in gas bubbles underneath the gills before floating to the top of the water to spread.[1] Underwater gills and ballistospores suggest that its underwater adaption is a relatively recent one.[1]

When synthetically grown, P. aquatica are known to only fruit (produce stipe and cap) underwater. A study done in 2014 by one of the original authors of the discovery paper showed that this species only produces sporocarps when completely submerged under cold water.[6]

The mushrooms are found growing out of water-logged wood, silt, and gravel, a fine volcanic substrate, and was observed growing from youth to maturity completely underwater over 11 weeks.[1] The mushroom grows submerged under fast, cold, running water of the river.[1] The water is spring fed, aerated, and contains lots of woody debris and is shallow in depth.[1] They are found growing about a half a meter underneath the water.[3] The mushroom is also found growing on land in either grassy banks, or on gravel or water-logged wood next to the river.[3]

Though not enough is known about the species to consider it edible, scientist assume that it is a food source for small insects in the river.[2] Though the river has low levels of nitrogen, nitrogen-fixing cyanobacteria near mushroom discovery sites suggests they might provide a source of nitrogen.[7]

The taxonomy of the species is in reference to the habitat of the mushroom is found in. Aquatica is a Latin word meaning water or watery.[8]